Help! Been having issues with older model PS3...

[RYJAPE21]

I have an older model of the PS3 (20GB) which I got back when they first released them a few years ago; I've had zero problems with it until just recently: whenever I play a BD or a videogame the picture will suddenly freeze. I can hear the disc skipping around and oftentimes I am forced to shut the PS3 off manually because it is entirely frozen. Sometimes the screen goes black or the image will shudder and there's nothing I can do for it to continue.

Has anyone else encountered this problem? Could the system be overheated? (which doesn't make much sense given the fan). The first time it happened was when I was watching a blu-ray disc and I just assumed the disc was faulty (especially when I was able to watch a full DVD afterwards) but then today when I tried a videogame the same thing happened (as well as a fresh BD). Anyone know what this problem could be or how to fix it? Any info would be much appreciated, thanks.