|"I recently had to reload XP ..."|
Whenever you load Windows from a regular Windows CD (or DVD) from scratch, after Setup is finished you must load the drivers for the mboard, particularly the main chipset drivers, in order for Windows to have the proper drivers for and information about your mboard hardware, including it's AGP or PCI-E, ACPI, USB 2.0 if it has it, and hard drive controller support. If you have a generic system and have the CD that came with the mboard, all the necessary drivers are on it. If you load drivers from the web, brand name system builders and mboard makers often DO NOT have the main chipset drivers listed in the downloads for your model - in that case you must go to the maker of the main chipset's web site, get the drivers, and load them.
This is especially important for laptop main chipsets!
When you first connect it, Windows doesn't recognize the wireless USB mouse directly - it recognizes only the receiver for it. You have to either active a tiny momentary switch on the mouse itself, and/or use Logitech software to get it to detect it, then it works fine. Of course, the battery or batteries in the mouse must have enough poop, and the mouse must be switched on if it has a switch.
If you tell us the model of the mouse we could probably find specific support info - or - read the installtion instructions if you have them! They may be on the CD that came with the mouse.
If that doesn't help
USB devices may not work correctly when they're connected to certain USB ports, e.g. ports in a hub or on the front of a desktop case.
This also tells you how to re-load the USB stack properly if you have an IRQ sharing problem you need to fix, but as far as I know you can only have that problem with a desktop mboard.
See response 3 in this: