Try this Reinstallation Technique and delete your LW preferences folder also, but make sure you back up the Downloads(.bak) file & return it only after you have re-installed LW & LW is closed. If same issue, try steps 5 & 6 in fixes for LW thread re: run as admin & change compatibility mode.

In step 2, that link seems to be dead, thus other offline installers for LW can be found in Birdy's post: here.