computer help please,,rampant mouse

I have an uncontrollable curser
that will run continuously across any data entry screen
on my PC.

leaving a trail of commas
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

this also happens booting to a Dos Floppy

thinking it may be a hardware or Bios setting prob??

anyway Using XP pro SP2
Asus A7V400..Sempron2800..PS2.Optical Mouse.

I have reloaded mouse drivers and reinstalled the OS.

any DLLs I can reload or registry tweaks that may help.

any tech links I may try?

thinks I will email ASUS
cheers
john