Has anything else unusual been happening recently? Have you tried giving your computer a scan with both Avira and
MalwareBytes' Anti-Malware? How long has it been happening?
Anyway, you might want to try this:
->Reboot your computer into Safe Mode (Hold F8 before the Windows 7 logo appears and choose it in the menu).
->Hold the Windows key, then press R. The Run Command dialogue box opens. Release the Windows key.
->Type the following and press enter:
msiexec /regserver
->Reboot back into normal mode and try again.
If
that doesn't work, you can try your luck with
this Microsoft Knowledge Base article - The Run command isn't available by default in Vista, but you can substitute it for holding the Windows key and pressing R, as above.