Have you tried reverting to a previous Windows restore point? To do that, you need to insert a recovery disk if you have it, or press F8 (can't remember which key it is) or some such while booting and select a recovery partition if you have it.

If that fails, perhaps forcing the BIOS to reset itself might do the trick. Typically laptops have a somewhat inaccessible reset button (you'll need a toothpick or needle or something similar) on the back (the bottom of the machine)... The manual of your laptop should mention it.