Audio/Video being strange

I didn't know what catergory to put this in but anyway

So, a few days ago watching videos online was absolutely fine
Now, I can watch videos if they're like 2 minutes long, if I try to watch longer videos like 5 minutes upwards, the video is increadibly slow which misses frames and pauses and the sound doesn't come through apart from a staticy type noise through the speakers.
It's not my connection because I've had the same connection throughout my internet using and it has been fine up to now. I've tried waiting until it has fully downloaded but it doesn't change. It doesn't matter which website either, it's all the same
I'm using Windows XP Professional SP3 or something along those lines. The only new thing I've downloaded has been BearShare. There are no virus's on the computer either.
Please someone help

Thanks