PC Booting Oddness

Hi - strange problem. PC ( Gigabyte GA-8PENXP, P4 3.0GHz, 1GB RAM, NVIDIA 5950 ) is having problems booting over thelast few days, hit the power button briefly spins the fans and then stops booting, screen never actually shows POST.

Unplug PS2 port mouse or keyboard, pull power lead and re-attach try booting again without mouse and it starts to boot, I can then quickly pop in the mouse and it continues to Windows XP Pro fine. Thought it was an issue with the mouse so tried a different one, no joy.

Then this evening went through the usual routine and the PC refused to boot, so I thought I'll just unplug the mouse and see if it'll boot fine with it in USB port. This still didn't sort it. So I figured just let it boot without mouse and just get the PC up and going....oddly PC didn't boot with my usual workaround. Wound up having to leave it for about 5 -10 minutes without power lead attached and I was able to persuade it to start, now beginning to worry it's a mobo issue or possibly a PSU problem.

Thoughts more than welcome.
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Very many possibilitys.  Memory, motherboard or bios.  First Reset the bios/cmos by removing the cmos battery, and then waiting a few second and replacing it.   This will reset to defaults.  

If that dosent work, test the memory, if you can get the machine to get past POST, boot from the cd-rom to memtest86, and let it test the memory.  If that doesnt work, it may be a hardware motherboard related problem.

real odd that it wouldnt post then it does post... have you had anymore post problems? can u replicate them everytime?
i also would look at ram... possible high density problem, if you have more than 1 stick, remove all but 1.
make sure your inside connections are all good, even power. ive seen post troubles before with new nvidia cards due to the 2nd power connector....
are you using IDE or SATA or SCSI for hd.
is it under warranty?
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Most problems booting intermittently are due to power supply problems, specifically needing to wait a little while before being able to boot.  Replace it with a similar-rated or more powerful unit.

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AlbertDongAuthor Commented:
virtuoso1 - tried clearing CMOS no joy....will give memtest86 a try tomorrow.

ViRoy - no other POST issues, this problem occurs each time I boot at the moment. Have done a good check of connections internally just making sure they are all seated correctly, looks fine. Will try the memory stick swap out tomorrow morning.

Callandor - must admit I feel like it's a PSU problem, fact that I've had to let the system sit for 5-10 mins before being able to boot is suggesting that to me aswell. Will try the two other suggestions tomorrow a.m....but think I'll be buying a decent quality PSU in the afternoon.

Thanks for help guys..will let you know how it goes.
I had an issue with a client's computer with almost the same exact problem.  Fixed it by changing the stock power supply with something like this: http://www.newegg.com/app/ViewProductDesc.asp?description=17-103-908&depa=0

That's one thing that people ignore when they are building a good box, the PSU!  I suggest getting a brand name PSU and don't mess with the $20 dollar cheapos.

Also, check your case for any shorts, like metal washers or loose metal pieces touching the mobo.  Might want to try running the mobo OUTSIDE the case just to make rule out that there is no shorts on the case.  

Good luck!
Two good calculators: assess your system power needs...
Please do not plug-in or unplug a PS/2 mouse or keyboard with the power on.  Doing so can damage your motherboard and make your problems more difficult to diagnose.  Its possible you now have more problems than originally posted because of plugging in the mouse with the power on.  Your original problem sounds like a resource problem.  Some piece of hardware wants to use IRQ12 (PS/2 mouse port) and is causing a conflict.  Remove everthing except RAM, video, and floppy/hard drive.  Does it boot?  Reseat all memory, cables, power connectors and your CPU.  Try again - any luck?
Sounds just like power supply problems I had recently.  Have you upgraded your video card recently?  The latest video cards can take much more power than in days gone by and an upgrade can put you over the limit.
Power supply for sure ..... Go buy one thast is returnable from a big chain store to test it..... its easyer than legos.
AlbertDongAuthor Commented:
Thanks guys - bought a more powerful PSU ( 650 watt ) now booting reliably time after time.
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