Movie Slow need help, please

My laptop with a Celeron inside. I downloaded a AVI movie then played on my laptop, it played normal but after about 15 minutes or so, the movie started getting slow. The action of the actors are slower than the conversation. Basically, it is slow. So I formatted it and reinstall everything, as well as update to Service Pack 2, then I tried to put on every single CDR that I recorded the movie into the drive, the same problem existed. I am so frustrated now, anyone out there could help me with this matter? I will appreciate that .

 

I am looking forward to hearing from you guys.