Is this recent ?

Are they plugged into the correct socket or even, dare I say it, turned on ?

Have you tried them on a friend's PC, do they work on his/her PC ? If same
problem, then they're buggered.

What soundcard do you have ? Have you tried re-installing the drivers ? Get
the latest XP specific ones from the manufacturer's website.

What did you do/install prior to everying going pear shaped ? If some
software has upset/corrupted a file, run your anti-virus then do a system
restore.

Is your soundcard recognised by XP ? To find out right click on My Computer

its not or is recognised but with a yellow triangle against, you need to
re-install your drivers.

Re-post once you've tried all thate above if still nothing.

Cheers,
Jerry