well shit, if it's the speakers it came with, you should have no problems at all... is it a headphone type-jack (type of plug most headphones plug in with)? if so, make sure they have power (if there's a seperate power cord) and plug it into a stero or cd player (in the headphone jack) and turn on the device (stero/cd player) and see if they work (assuming everything is plugged into the speakers, if they don't have an additional power plug it should still work) and tell me if works...

if they're the ones that came with the computer, there should be no real problem (unless you installed a new sound card into the computer), so have you installed a new sound card into the comp? (you'd know if you did or not... it's hardware, or 'computer components' if you will..)

stupid question, but they HAVE worked on your comp at one point right? answer these questions and get back to me.