my mouse stops working??

[CtK]

my specs are below

im using a Microsoft Intellimouse Optical
it doesnt say any version on the bottom

after i play Dungeon Siege for like 2 hours it totally stops working
it will work in the USB but not in the PS/2 port

anyone know why this is happening is my mouse dying or my PS/2 port on my MB??

please help
thanks

 

[TRUCKMAN]

have you been cmos to see if the ps/2 port is on/off when that happens?????