Boot problems after processor upgrade

I have a Dell E521 with Vista and recently decided to upgrade my processor from an AMD 3600+ to a 5600+, which as far as I could tell went fine. For the first few days I had no problem; the CPU was recognised and worked fine but then I started getting the an error message when trying to boot up - "Windows failed to start. This may be due to a recent hardware or software change" with the following details:

File: \Boot\BCD
Status: Oxc000000f
Info: Error occurred while attempting to read boot configuration data

The message also said to fix problem by booting from installation disc and choosing repair and restart. This worked fine but I still got the same error message if i tried to boot from hard drive. I'd heard that other people who'd changed processors had similar problems and they recommended updating bios and clearing cmos. I tried updating bios again with no effect and then tried clearing cmos by removing battery from motherboard, unfortunately this seems to have made the problem worse! I now can't even boot from disc as Windows crashes just before the Vista screen which asks you if you want to do a fresh install or repair your computer.

I'm now very confused and would really appreciate any help.

Cheers