AVI's speeding up

Hi there
Strange thing began to happen last night. I was going to watch an avi I downloaded last night. On the computer I downloaded it too, it seemed fine. i skipped ahead to different spots and it was playing fine all in sync. I copied it to my laptop desktop and started watching it. played fine for a while then all the action speeded up and off course the audio went out of sync. I downloaded the latest codec pack and began again. where it sppeded up before worked fine but it happened a few minutes later. I switched to a dvd with that and four other programs on it. same thing happened at a different spot. change to aother program on the disc and it worked fine until the end when it too speeded up a bit. This was all done using windows media player and I haven't had time to try another player yet. But does anyone know what would cause this too happen?
brent

So it happens with all avi's and dvd's? or just one or some?

You already have one other player to try out on the computer if it's xp. try clicking start>run [type] mplayer2

to get an older version of WMP.

it seems to be hit and miss. I have a DVD with 5 avi's on it. They all work fine and in sync on the machine I burn from. one in particular is acting very strange while two others speed up near the end. I file copied this avi from the desktop to my laptop and same thing. I tried playing it on the laptop from the file on the desktop and it worked fine but when i tried to play it on my TV thru s-vid it sped up again. I tried it on nero 7 and the same thing happened. will try mplayer 2 later on today.
i also have one that works fine on the desktop from a folder onthe desktop but once burned as an avi, it says it can't play due to the wrong codec. is it not just a digital copy, should it not work just fine. maybe the dvd burner is the culprit...