Is there any obvious damage to the dvd? Can you drag the progress indicator of your player past the stop point and resume play? Can you copy the file to your HDD?
Most of the free tools that you can find via Google seem very old and not particularly effective. Wmv is not really a video enthusiast's choice so repair apps are limited. From my googling I'd try
Steeper which is a GUI version of ASFCut. Those old apps were written for XP and earlier so may not run on your (unspecified) OS. Make sure you check for viruses in those old small progs.
I usually run what is now DiskSpeed, Scan Disc tab to see if there are error on a disk rather than corrupt video. You can find the old free version
here but you may as well try to recover the file first.