Question : Problem: Video rendering on avi, wmv and mpg files going bad

My monitor otherwise shows good video output. Within the last week however, video files like mpg, mpeg, avi and wmv have deteriorated. Depending on the file type I'm getting black snow or green flakes. I haven't made any changes to my computer's configuration. What could be going on here and how can I solve the problem?

Answer : Problem: Video rendering on avi, wmv and mpg files going bad

Actually, I was not talking about the cpu fan but the GPU fan. This is the one that is on the video card itself cooling the memory and/or chip. You will have to open your case and actually watch this spin up while you stress it as it usually smaller and relatively soundless unless you have a monster video card.  Artifacts are often an indicator of an overheating card and if yours turns out to be a dead fan then this can easily be replaced without buying a new card. On the other hand, your new info about movies  from u tube is good new info. They use flash codexes .flv  On the other hand, they are usually smaller lower quality files though that may not stress the gpu as much as the other codex's you mentioned. So I am still leaning  towards a vid card issue.  

http://www.softpedia.com/get/System/Benchmarks/Video-Card-Stability-Test.shtml
This is a free one but what is your video card in question as I could recomend a more mainstream one if I knew it. Many free over clocking utilities will naturally include stress testers to guage the stability of an overclock. Some of these are ati or nvidia specific though.