Set defaults in BIOS to enable USB Controllers
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I had exactly the same problem , when I reinstalled Windows XP(SP2) on my friend's computer:
USB Controllers were not listed in Device Manager.
It was MDG system with Intel's integrated motherboard.
I think integrated motherboard caused the problem.
I was reinstalling Windows from desk top maker's CD.
They recommend to install chipset driver and BIOS update first thing after complete reinstall,
but that did not resolve the issue.
I spent almost 2 days trying to find solution. I searched Google and tried everything I found on differnet forums and Microsoft website, installing .NET Framework and other available updates. Nothing worked.
I knew I had to re-enable USB in BIOS.
But when in BIOS, I could not modify entry for USB, it did not allow me to do that.
I was not allowed to select USB on Advanced tab.
SO I just selected Set Defaults (F9), and immediately I could see that USB was enabled. I saved and restarted the computer...
The problem was resolved. After restart, the system found USB controllers and installed them.
PS : Microsoft claims the problem can be resolved by installing Windows updates, but it never did.
I noticed this problem is quite "popular". I personally went through 20 or more sites.
PS: another workaround: to buy separate USB (2 or 4 ports) card, if 1st solution does not help.
Good luck! I know what you feel!