Keyboard and mouse randomly stop working. Possible causes?

[Wrecklusive]

My girlfriend's computer. Her mouse and keyboard stop working, at random, it seems. She can reboot her computer, and they can work for 5 minutes or 2 hours, but eventually they stop responding. Sometimes it's both, sometimes it's just the keyboard. Sometimes the computer continues to run, other times it locks up.

I'm not an expert at computers, but I know a bit (I've put together a few). After some preliminary fixes that did not work, I did a complete format and reinstall of Win7, reset the BIOS with jumpers/battery. I also did a mem test for the hard drive which checked out okay. The problem still persists.

Right now I'm guessing it's either a faulty/failing motherboard or PSU. Would one of these be the likely culprit, or are there other possibilities? Tomorrow I plan on trying a different PSU, and possibly a different MB if I can find an old one that works.

Any possible causes, solutions, or general troubleshooting advice is much appreciated, thank you.

 

[Nocens]

What do you mean "mem test for the hard drive"? Did you run memtest86 yet to test the memory (RAM)? If not then definitely try that.

http://www.memtest86.com/
Just click on free download and burn your own CD. It is a bootable test.

 

[AP514]

assume'n your stuff is USB...make sure to check out system/Device Manager..see if you have any problems under --usb hub. I would install latest drivers. Also some times the device stopps working from system going into sleep mode...

 

[Wrecklusive]

I ran a hard drive test and a RAM test, both check out fine. When I boot Windows in safe mode, the problem doesn't seem to occur at all. Any ideas what this points to? I installed all the most recent drivers for the MB.

Oh, I forgot to mention, it's not just the keyboard/mouse. I thought it was, but the PC completely locks up/freezes. The lights of the keyboard/mouse go off at the same time. The screen stays up and just freezes, and if playing a video or something with sound, it will go into repeated audio stuttering.