My mouse is stuck. When I boot up my pc, my mouse won't budge. Any suggestions as to what the problem may be?

I have a Dell and a Compac pc that was given to me for repair, and I have no clue as to what other problems I may encounter. They both are running Windows XP Pro and Home Edition. The keyboard is working on both. The mouse, keyboard, soundcard, video card, etc. are all on the system board. Please help! I can do most repairs myself and I do not want to put them in the shop because they are older computers.|||try takin the rubber ball out of the mouse,after alot of use,sometimes garbage gets buit up where the ball rides,if that does not work,check the properties of the mouse,it may be bad.|||have you tried unplugging the mouse, then firmly plug it back in and reboot? happened to me.|||sometimes when my mouse doesn't move all i have 2 do is click one of the buttons and it's fine