USB ports work on BIOS and boot, stop working on XP startup

I have a computer that is currently running Windows XP SP2. This machine is a Dell Dimension 510. It only has USB ports for keyboard and mouse - there are no PS2 ports available as is from the manufacturer.

I am able to utilize the USB keyboard during boot sequence. I even tried a wireless USB keyboard, and it works fine during the boot sequence. However, once the Windows XP User Select / Login screen comes up, the USB keyboard and mouse stop working. Ports are still receiving power as confirmed by digital multimeter. I ran a boot CD, booting into Ubuntu, and the USB keyboard and mouse work just fine there --> This confirms that this is NOT a hardware related issue. I have unplugged the machine and let it sit for several minutes, comes back up and does the same thing. I am unable to test PS2 keyboards as this machine does not support PS2. I have tried all USB ports and have tried different keyboard / mice combinations. Once you get to the XP User Select / Login screen, the USB mouse and keyboard stop working.

If you need any additional information, please let me know and I will be happy to supply. Any idea what may be the cause of this, and how to resolve?
 
A few comments
I am able to utilize the USB keyboard during boot sequence.
That's because BIOS provides USB support up until the time Windows starts. So this plus the fact it works when you boot into Ubuntu all point to a Windows problem

I'd suggest two things
1. You should upgrade to SP3. See [post=744411]USB Device Problems? Check for Windows Updates[/post]

2. See [post=751005]How to Reinstall Your USB Controllers and Motherboard Chipset Drivers[/post]
 
I upgraded to SP3 and during the process, encountered some corrupted files that may have contributed to this.

I performed a Repair Installation and all is performing as required.
 
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