How do I get computer to see USB external drives?

I  tweaked my system using the services configurations recommended by blackviper.com

I *NEVER* do these things.  

Go to your computer manufacturer and see if they have USB / USB Controller Drivers that you can download and re-apply. If they do, and you do re-apply, shut the computer off, start up and test.

Another thing to try is System File Checker. Open an admin command prompt and run SFC /SCANNOW twice. Allow to complete, restart and test.

Check device management to see whether the drives are listed there, but they do not show up in my computer, because they do not have a drive letter associated with it.
Unknown device means that either the USB mass storage that you are using is not one for which windows 7 has drivers ( you would need to install the drivers) or the USB mass storage is no longer functioning as the day it was bought, they too might go bad.

The issue could be that the mass storage device you use requires more juice that can be drawn from the USB port if it is powered through the same connection as it is transferring data, i.e. there is a second power only USB cable that needs to be plugged in or the use of an external power source is needed.

Does this USB storage work anywhere else?

I have a number of external drive - none of them work on this computer.

Other USB Devices work fine, just not the  external drives.  They all work on other computers

The registry tweaker may have screwed things up (not uncommon).

Try System File Checker as noted above.

Do you see the drives in Disk Management (right click on Computer and select Manage)?

I think you disabled the USB enumerator function i.e. denying all except HID devices. which presumably keyboard/mouse plugged into these USB ports are detected and work?

either within the registry or using the local security group policy.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor is start set to 3? or 4? if 4 change to 3. and see if the behavior changes.

Do you see the drives in Disk Management (right click on Computer and select Manage)?  
>no they do not show

I tried the system file checker - did not resolve.

If you tried the registry entry suggested and that did not work, then you may need to try a Windows Repair Install with the Windows 7 DVD.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor is start set to 3? or 4? if 4 change to 3. and see if the behavior changes.

>see attached keys are these correct?
C--Users-Paul-Corathers-Documents-Captur

If you tried the registry entry suggested and that did not work, then you may need to try a Windows Repair Install with the Windows 7 DVD.

>I was hoping that was another solution. :(

Tools that muck about with the registry can wreck a system. I do not know of another solution to fix a registry if SFC does not fix it.

I want to back up my system before doing a reinstall but without the external drive, that is a problem.

I've used system tweaks to great success but this time - it looks like it messed it up,  and no backup. :(

If no external drive works, then you can (a) map to another system and back up documents or (b) use USB keys to back up documents.

Reinstall the USB drivers. Also try to connect a USB stick - will it be detected?

I think you disabled the USB enumerator function i.e. denying all except HID devices. which presumably keyboard/mouse plugged into these USB ports are detected and work?

>that is correct all other USB devices are OK!

Reinstall the USB drivers.
>How would I do that?
Also try to connect a USB stick - will it be detected?
>it does  not see any external drives including "sticks"

USB disks usually need quite a bit of power. Maybe your PC can't supply enough power via the USB ports. Do your USB disks have an external PSU? If not, does the cable have two USB connections for the PC side? If yes, use both connections. Usually one of these connections is just for power, while the other is for data and power..

Also check in disk management. If the disk is seen there, it may just not have been assigned a drive letter. You can do that yourself within diskmanagement.

Does a USB stick work? Maybe an auotmount for USB drives is simply disabled and they are waiting for you to assign a drive letter.

Do you have an anti-virus internet security app within which usb storage was disabled?
Check the event viewer log to see what it reports in system and application when a storage usb is attached.

This is called re-install USB driver.

I am glad that the information provided helped you resolve the issue.

>This is called re-install USB driver.
I asked you "how do I do that?"  but I did not get an answer.

Well, reinstalling is recommended when the drive or other usb devices such us phone, printer etc are not detected. Wanted to be sure if that is the problem, like checking the drive in Windows Disk Management. Like a doctor who asks questions before prescribing amputation. Not my style of assistance suggesting all possible solutions that may work or may fail to help.

In my first comment https://www.experts-exchange.com/questions/28586755/How-do-I-get-computer-to-see-USB-external-drives.html?anchorAnswerId=40517683#a40517683 the suggestion to check device manager was made. You made no mention that something was there out of their dinars like the unknown device.
Usually there should not be any exclamation or yellow question mark labeled devices/components in the device manager display.

You are the eyes and ears for the experts who suggest a course f action in hope that you would follow and provide responses ....

John's solution got me started in resolving the problem.  It was incomplete. I had to spend additional research and time to solve it myself.