USB Port Problems

Had some troubles with my computer turning itself off, so I called Dell tech support and they sent someone to fix it.  He replaced nearly everything on my computer except for the harddrive, the CPU, and the screen.  The problem is fixed, but now, my USB ports don't work.  I mean flat out don't work.  If I plug my mouse in it won't detect it, nor will it detect any other USB devices.  I tried updating my drivers, uninstalling and reinstalling the USB ports, a system restore, and nothing works.  Weirdly, the mouse (its optical) will light up when its plugged in sometimes, but still does not work.  Everything else on the back of the computer (network cable, power cord) works fine.  The tech support guy told me I'd have to reinstall Windows etc, which sounds ridiculous to me.  I have a suspision that the tech support guy who came to fix it messed something up when he put it back together, since the USBs worked fine before he did anytihng.  Any ideas on how to fix this?  I updated the BIOS and everything.  Thank you so much!