What model PS3 have you got, Fat/Slim?
Before I got my slim my my fat PS3 decided to packup it was freezing and wouldnt read disks. After reading several forum topics and viewing several youtube videos I found out that it was the laser in the bluray drive and that this is quite a common problem with the older Fat consoles.
If it is this problem there are plenty videos which show you how to clean the lense on the laser on youtube. I tried this on mine but it didnt work, so the options I had were buy a new bluray drive for what I thought to be a LOT of money or sell your PS3 on ebay and use the cash the buy a new slimline model.
This might not even be the issue but hope this helps