Microsoft's knowledge base recommends updating the driver (or reinstalling if it's not there).
If tech support have been p***ing around with your PC then chances are something's worse than before!
Go into device manager where you were before (I assume) - Start -> control panel -> System -> Hardware -> Device Manager. Find the AC97 component, right click and go to 'Update Driver'. If you have your motherboard driver CD then bung that in the drive at the same time. Alternatively just bung teh CD in and let it install the driver. Difficult to tell more without seeing it (no I'm not coming to Lancs either
)
Good luck!
Rob