Doctor Who,
It might be the site providing the movie.? Too many viewers and not enough machine? Try another Movie site?
1) Clean your machine
2) Shut down open windows not needed; disable unneeded startup programs. Msconfig ?
3) Not enough Ram?
4) Slow CPU?
5) Wrong Video Card?
6) Check with Computer Manufacturer's support
7) Virus?
Try a new DVD Movie for the DVD problem?
9) Unplug from wall and reboot? ( Might need to plug back in before the reboot? )
10) Talk to your machine; encourage your machine