Several ways to fix that, I would say Restore to a point with no errors if you have it.
Re-install the last service pack. Search web for Services List and restore what services are on and starting for your OS. Add Windows components from install disk, overwriting ones already installed. Run Command Prompt - sfc /scannow.
Run Virus/Anti-Spyware/Anti-Rootkit full with no exclusions. Do a fresh install of windows, re-register programs to new install, delete old Windows directory.
When all else fails - re-partition, re-format, re-install fresh windows.