Windows 7 keeps freezing, disconnecting/reconnecting USB devices

Question

Last week, a lightning strike near where I live caused a power surge and as a result, my ethernet card was fried.  I took my computer (iMac) to a store to have it repaired, and they wound up replacing the entire motherboard (a bit extreme in my opinion, but what do I know).
When I got it back today, sure the ethernet problem was solved, but I noticed that my taskbar was acting weird - specifically the icons in the notification tray.  Lots of them were "blank", meaning there were just empty spaces that would highlight when I hovered the cursor over them, but nothing happened when I clicked them.
Then I discovered that clicking any of the icons in the notification tray almost immediately froze the computer.  Frozen, as in completely unresponsive to the point where my only option was to manually shut off the computer.  That happened twice.
My solution was to reboot in safe mode and run system restore to an earlier point.  That fixed the notification tray problem (no more freezing, and the icons were all back), but the computer still keeps freezing at random intervals.  Again, my only solution is to manually shut it off by holding down the power button, which I hate doing because I know it's bad for the hard drive.  Sometimes it froze as soon as the welcome screen.  I tried running a virus scan, but again it froze in the middle of the process.
On top of the constant freezing, it keeps disconnecting/reconnecting my usb devices.  My mouse and keyboard will suddenly drop out for five seconds and then start working again.  This constantly happens, to the tune of several "disconnect" sounds playing over the speakers.
What the heck is going on?  I tried re-installing the Boot Camp drivers, but that didn't work.  I have my Windows 7 CD and backed up files, so if worse comes to worst I can do a clean install of Windows, but I'd rather not have to spend a day re-building my computer, and I'd REALLY rather not take it back in for another repair, since that took a week and I need this for my work.
Any ideas on what I should do?  I'm out of town on my laptop for the weekend, and I'd like to have a game plan for when I get back.

Answer 1

I'm very excited to finally have a solution for this problem. Thank You Balaji for figuring this out. I've been struggling with this for a number of years, and had only one USB Hard Drive that worked. I too have VMware workstation, and had the missing files
in "c:\windows\inf." I can say with certainty that I did not delete the files from that folder, but something is common in both of our situations. Maybe it has to do with VMware, and some of it's updates over the years. I'm also using nCompute to share out
a networked desktop via the wire. 
One more thing worthy of mention is this machine was an update from Windows Vista, and the USB hard drive that worked was configured back than. So although I could never add another HD, at least I had the one.
Now with having copied over the files, I can plugin other USB enclosures with different drives and they too are working.
Like you mentioned, it was always possible to use USB devices within my Virtual Machines, so it was clear that the USB ports were functional. I actually got the files from a clean Windows 7 VM, copying out the \windows\inf folder and doing a compare between
the the real one and the virtual one. I found the two missing files you mentioned, along with 8 others. I went ahead and included them all in your fix.
It worked, Amazing. Thanks again. :O)