Can anyone help me?

When ever I shutdown my computer the bios clock stops. This affects both windows and dos.

I can't think why this would be happening because the bios does not loose its other settings.

The problem doesn't occur when I restart so I assume it is something to do with the bios battery. However I'm not convinced because the bios doesn't loose its other settings!

Any ideas would be much apreciated
Thanks
Nathan Winters.