Stain

Well whenever im playing it would freeze from like 5-30 min of gameplay. My ps3 also sometimes wouldn't turn on, the lights at the front of the ps3 light up as they always do but it wont show anything up on my screen it would just be black. Whenever my ps3 freezes i can still see the screen and everything that i was doing but i cant move anything with my controller it basically just freezes. On the back where it says digital out (optical) it shows a red glow from inside dont know if thats worth mentioning but meh. I have had the ps3 for about 2 months but i baught it off the internet and it was used so i dont know how old it really is. Does anyone know how to fix this?