As above: try removing the Media Player via from "Programs & Features" -> Windows Features, reboot, then add it again & reboot.
Or just use VLC. I never use WMP.
If you have System Restore enabled & haven't deleted restore points, try restoring to a point before the malware infection. Make a backup first though.
Or try Sysinternals' Process Monitor (
http://live.sysinternals.com/procmon.exe) to try to figure out what it's trying to find (file or registry entry) and failing on - then either putting the file back or copying the registry entry from another PC. Win7 can be used fine when unactivated for a very long time, and perhaps you could put the second copy in a virtual machine. If you don't have the resources for that, I don't mind either getting the entries or files from my Win7 x64 PC or putting Win7 x32 into a VM - I have a Technet subscription for just this kind of stuff.