New mobo and processor= Reformatting????

[TheMajor]

Complete re-install is the best.
Often works without re-formatting, though. May require repair install.
Always backup.

 

[Meithan]

If it's not too much trouble to backup your sensitive data, then I'd definitely just reformat and reinstall Windows. Having a fresh install is always nice.

Besides, I don't trust the Windows repair tool with a major change such as the CPU & mobo.