Windows re-install question

I have a Compaq/HP Laptop and I'vebeen having various problems recently. One
of the options is a Windows repair procedure. The other is a re-install
procedure which includes a reformat. The original installation was SP2 but
SP3 has subsequently been installed (not by me). Would this mean that
either/both these methods would screw up the operation?

Before anyone suggests uninstalling SP3 first, I've already tried this
through Add/Remove programs and that operation was halted because "Couldn't
locate file"!

Regards and thanks in advance

Pat Macguire