USB ports not working

[cha59]

I had a problem with my USB ports not working. I plugged a flash drive in that had previously worked fine and the computer would not recognize it. Then I tried another flash drive and it didnt work either. I plugged both into a different computer and they both work fine. My external hard drive and camera wouldnt work either. I tried all of these items in multiple ports and nothing worked. The weird thing is my printer, keyboard and mouse worked fine off usb ports this whole time.

I called Dell and they were able to uninstall all my USB ports and reinstall them. When they did this, the USB devices all worked - for only about 12 hours. Now I have the same problem again.

I am aware that when using a USB device it is wise to use the "safely remove hardware" button any time you remove it from the computer.

I run McAfee anti-virus and firewall, have a router, run two solid spyware programs and it does not appear that I have any viruses or anything like that.

What else could be causing this? What should I do? I can call Dell and have them do the same thing over again, but it looks like that is not a permanent solution.

FWIW I have a Dell Dimension 8400 with Windows XP. It has a 3.2 ghz processor and 4 GB of RAM. I've had it two and a half years and never had USB problems before.