First thing to do: look at the event log of your PC to see more on what went wrong. Post your findings.
Also tell more on what happens: does the video crash, does quicktime crash, does the PC crash? Blue screen of death? What error number?
Also tell something about your hardware and OS.
Ive been having this problem for a while. All most all the time when watching videos if its on youtube, quicktime, or any video on or off the web it crashes? Tell me what i need to do to resolve this its really annoying thanks in advance