BleepingComputer.com: Mouse And Keyboard

Hello guys. My grandmother has this old pc with XP home installed into it (don't know the specs, but it must be a p3, with no more than 256 ram and around 20 gb HD).
She has this old keyboard and mouse, so she decided to change her old mouse for a noew optic mouse. The problem is that, when she plugged the new mouse, the keyboard got "disconected". I mean, the comp. didn't recognize it and didn´t boot (of course). I, then, unplugged the mouse, plugged only the keyboard and booted XP, then plugged the mouse and let XP recognize the "plug n play".
After that, i rebooted, everything was fine, until i tried to type anything. voilá, the keyboard was conected, but didnt work. The bios detected the keyboard, for windows was running. But windows itself did not detect the keyboard (my guess). I checked the keyboard icon in control panel, but it didn't give any useful info (no properties, no problem solving provided either).

I'm lost in what to do now. I plugged the old mouse back, but then the comp. didn't recognize the keyboard again. Can it be an incompatibility problem between mouse and keyboard? Can it be that the drivers of the keyboard just got deleted?

Anything will be useful, as for i don't know what else to do, and don't know very well the origin of the problem itself.

Is the new mouse USB or PS/2? Is the keyboard PS/2 or USB?

Regards,
TheYoda

oh yeah, sorry.
The keyoard is PS/2, the mouse is USB, but also has the PS/2 adapter. I just plugged it with the USB.

Try the mouse with the PS/2 adapter. see if that works