Vista - Rundll

Everytime that I try to open or click on a video file to play it I get the
message
"Windows Host Prosess (rundll32) has stopped working" "windows is checking
for a solution to the problem" and then another window pops up stating that "
A problem caused the program to stop working correctly. Windows will close
the program and notify you if a solution is available"
I haven't got a notification to what the problem is if anyone knows please
help.