I believe at this point you need to answer this question posed earlier by jj3000 "What's the brand and model of this computer?". Given that you said it is very old it may well be to start with that it will NOT allow the use of 2.0 USB devices as it may have only been capable of 1.0 . Sometimes a 2.0 device will operate on 1.0 usb ports and sometime they won't. I don't believe that if they are 1.0 that they can be upgraded to 2.0. To determine your brand and model of computer try an Everest scan and see what it brings up on that score.
http://www.softpedia.com/get/System/System-Info/Everest-Home-Edition.shtmltruenorth
Here is another link that deals with a missing serial bus controller:
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!
Credit to:
http://www.tomshardware.com/forum/51916-45-controller-missing-device-manager