Any idea why my mouse won't work?

I just got a used iMac (running 10.5.8) with the metal keyboard and mouse. I unpacked the box, plugged in the computer, hooked up the keyboard and mouse.

The computer screen came up. I can move around a little via the keyboard's arrow keys but the cursor will not move via the mouse. I got it to move a little by swiping my thumb across the back but that is it. I switched my older, working, keyboard and mouse to the newer machine and it didn't work there. I switched the newer metal keyboard and mouse my older iMac and they worked just fine. What could be going on with the new (but used) computer? I have tried every port for the mouse, keyboard as well as every back port but nothing moves the cursor.

Message was edited by: janedougall