Can't reinstall Mac OS X

Most likely your installation media is no good or the system logic board is having an issue preventing it from seeing the drive. Have you tried a USB drive? Additionally, this could be an unsupported OS install disk that you're trying to boot to. Is this a disk that came with the computer or is from somewhere else? Macs can also be finicky about what CD/DVD drives they will boot to as well.

If you have another Mac you can actually use Carbon Copy Cloner to clone a good OS install disk to an external drive or USB keychain (assuming this is a model Mac that will boot to USB). Then, you can try booting the installer from the external hard drive.

Renazonse is correct that the most likely explanation, barring some hardware failure is that the version of the OS you are trying to install isn't compatible with the Mac.  Here are the basics. Any Mac can ONLY install an OS X version that is no older than what came on it.  So if it came with Mountain Lion, you can't install Snow Leopard.

Second, there are two types of disks. There is a version that came with the Mac and should have on it the model of the Mac it was made for. So if you have a disk that says Mac Mini it can't be used on a MacBook Pro. The other type of disk is a retail version that will work on any Mac as long as it's no older than the version that came with the Mac - see paragraph one.  If you are trying to use the last couple of versions they are only available on-line through the Mac App Store, although it is possible to create installer disks for them. If you have a friend who has a Lion, ML, or Mavericks install disk you could try that... and it should work as long as the hardware isn't too old to install on.

You can get the model number of the Mac by typing in the serial number here:

http://www.everymac.com/ultimate-mac-lookup/

That site should also tell you what is the oldest software that will boot that Mac.

Can you scan an image of the DVD and post a jpg so we can figure out what you are using?

It's the disc that came with it, pretty sure it's Mountain Lion but i'll check.

Mountain Lion didn't come with optical install media. They had moved to the internet or usb keychain drive delivery by that time. So, if you have a DVD of it it could be a bad disc.

Sorry it's actually 10.6.2, Snow Leopard.

There's also an Applications Install DVD which says to hold down the D key at startup to use the Apple Hardware Test but that doesn't work either.

What's the serial number or model number of this machine? It may just need a PMU reset to correct the issue and I need to model to dig up the correct key command to do it. Or, you can Google PMU reset and find the procedure for that model.

This is the iMac model from that link:


iMac "Core 2 Duo" 3.06 21.5-Inch (Late 2009)      3.06 GHz Core 2 Duo (E7600)
      
Intro Date:      October 20, 2009      Disc Date:      July 27, 2010
Order No:      MB950LL/A*      Model No:      A1311 (EMC 2308)
Subfamily:      Late 2009      Model ID:      iMac10,1
Std RAM:      4 GB      Std VRAM:      256 MB
Std Storage:      500 GB, 1 TB (7200 RPM)      Std Optical:      8X DL "SuperDrive"

To reset the SMC:

Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve

• Shut down the computer.
• Unplug the computer's power cord.
• Wait fifteen seconds.
• Attach the computer's power cord.
• Wait five seconds, then press the power button to turn on the computer.

Reset the PRAM:

Restart with the Command, Option, P, and R keys held down, and release them upon the second chime.

Pretty sure i tried that before but without the SMC reset so will try it now.

No luck, just get the same result, there's no second chime & i just get the no bootable device..... screen.
Could it be the keyboard?
I have a few Windows keyboards handy, would they work?

Sometimes Windows Keyboards work and sometimes they don't. The Windows key is the Command key. Not impossible that the keyboard is the issue but if the Mac can't find a bootable hard drive it would automatically boot the optical drive.

You may need to get a different copy of the OS install on an external disk to boot over USB or Firewire. If you've already replaced the optical drive you may be able to open this machine and look at the motherboard. These iMacs are notorious for having an issue with bulging capacitors on the board and the machine becomes useless after that. Those caps can be replaced if you know how to use a soldering iron and the machine will start working again if its not too bad off. If you see any slightly bulged or leaky caps on the board, it's dunzo.

You are not using a wireless keyboard by any chance? If so, try one that is connected by USB

It's a USB Keyboard.
If it's the board it's over my head to fix it.
I'll try a few keyboards & see if any of them work.
If not i have an old Macbook there, Model No: A1226, would i be able to copy the install disk to a USB key & use that to install? If so could u post step by step instructions?
Thanks for all the help btw.

Use Carbon Copy Cloner (free for download on the web) and clone the Disk you have to an external drive or USB key. It will erase the key.

Do you have a firewire cable? If so, you can connect the MacBook and the iMac using Firewire Target Disk Mode. This in effect treats the iMac as an external hard drive of the MacBook. You can then run Disk Utility from the MacBook to reformat the drive on the iMac.  Reformat it as Mac Extended Format (Journalled).

See:  http://support.apple.com/kb/HT1661?viewlocale=en_US&locale=en_US

You can also see if the MacBook will read the OS 6.2 DVD. It likely won't be able to boot from it, but at least you can find out if is a readable DVD.

You could try using Disk Utility from the MacBook to make a disk image of the OS 6.3 DVD, then restore the disk image back to a fresh DVD.  I think you will need a dual layer DVD.

Any possibility the new DVD drive was not installed correctly? Loose cable maybe?

You also maybe be able to install the OS directly using Target Disk Mode as per this article:

http://lowendmac.com/2006/installing-os-x-10-4-tiger-on-dvd-challenged-macs-using-firewire-target-disk-mode/

Here is another article with options for installing an OS on a computer with a non-functional DVD drive:

http://reviews.cnet.com/8301-13727_7-10399193-263.html

Obviously this is all on the assumption that the DVD itself is good.

Ok, lots to go through here so will start in the morning & post back the results then.
Thanks again for all the help.

Looks like i'm jinxed.
I went to charge up the Macbook & noticed the charger light went green immediately even though it hadn't been used in a good while. Left it overnight but it didn't charge & won't turn on so no other Mac to try most of the advice.
I did find an external DVD drive & tryed to boot the disc from that but no joy. Also disconnected the internal DVD & boot from the external but again no luck.
I'll grab a few keyboards today & try them. The one i had doesn't work at all.

Try resetting the SMU on the MacBook:

http://support.apple.com/kb/ht3964

Got a new charger for the Macbook this morning so back in action again.
Have checked the DVD in the Macbook & seems fine.
I've no Firewire cable but have a USB hard drive caddy so would be able to connect the iMac hard drive to the Macbook. Could i install directly from here?

You could try. There is a danger the DVD might sense the Mac that is doing the installing and install tailer the install for a MacBook rather than an iBook. worth a try, though.

Tryed to boot from the DVD but after entering language it the tells me that i can't install OS X on this device, or something similiar so didn't have the option of installing on the external hard drive.
Tryed to copy & paste the install folder from the disc to the external drive, put it back in the iMac and startted it up but no joy, just the same error message.
Would copying the files to a usb stick make any difference?

It may be that the MacBook is old enough that it still has the PowerPC instead of the Intel Chip. (Pull down the Apple Menu to About this Mac to find out). OS 10.6.2 won't install on a PPC chip Mac.

Alternatively, you are getting the message because the install disk is an OEM disk intended for an iMac and the disk checks the machine first to prevent piracy.

If the disk is grey, it is an OEM disk.

Here are instructions on how to make a bootable USB flash drive installer:

https://discussions.apple.com/thread/4155520

Another set of instructions: http://www.ihackintosh.com/2009/08/how-to-make-a-bootable-snow-leopard-usb-stick/

It's an Intel Dual Core.
Yeah the disc is grey so must be OEM.
I'm creating a bootable USB at the moment but keep getting an error "Restore Failure. An error (2) occured while copying. (No such file or directory)"
Any ideas?

Sounds like a bad dvd. Maybe that's why the iMac won't boot from it. Try carefully cleaning the dvd and try again. Also check for scratches.

I've managed to create a bootable USB drive through a Windows laptop using  Poweriso.
It works on the Macbook but when i insert it in the iMac and start holding the option key i don't get the boot option screen, just a black screen with a blinking white cursor in the top left.
Borrowing another usb apple keyboard 2moro so will see if that's the problem. Was told it's working fine and it does work at the "No bootable device -- insert boot disk and press any key" screen but maybe there's some problem with it.

It's doing that because its hooting a windows bootloader and does contain the required efi information to complete the boot. Sounds like you need a new OS installer.
http://mashable.com/2013/10/23/clean-install-os-x-mavericks/

As it was the keyboard that was the issue all along, nobody mentioned it but myself.