Seconding Arctic Silver.
Sure, it's possible. Especially if it ONLY happens in MPC. If it happens in others as well then of course it's not your media players. Are you using the latest official nVidia video drivers from their web site?
If I may comment at this late stage on this older reply of yours, the same codec(s) can be used by multiple media players, which is their advantage. I don't use MPC but I believe it still uses external (not built-in) codecs, so it might use the same codecs that PowerDVD does.
I'm not exstatic about your video card temperature, but if you finally determine that it's not that, then I would:
1. Figure out for sure if the problem is happening with more than one media player.
2. If it is, try to test/notice if it's the same type of videos that always have the problem (WMV, AVI, MPG...).
If it is, that would be fairly strong evidence it's a codec problem. I would defintiely encourage you to pursue the heat angle first, though.
Another simple test you can try is using a media player that doesn't use external codecs like
VLC (VideoLAN). I know you might be thinking that the very last thing you need is yet another piece of software or media player installed. Because it uses it's own built-in routines, it's great for avoiding codec conflicts and just plain having to install codecs at all.
I would install it, uncheck the option to associate itself with any videos/audios, and then choose Open With on a video and (uncheck to use by default) select VLC to try it on a video you know you've had the problem with.