Why can't my ps3 reproduce games?

**FAT PS3***So, thought it was YLOD(had the blinking red light), did the fix and applied a cheap thermal paste. Now it works fine for: cd, dvd, bluray ROM, netflix, dowloaded games such as infamous that most of us got back in the day, but it fails whenever I try to play a game(disc) and it turns off as the little blinking red bugger teases me yet again. What do I do? Is it the cheap thermal paste? Should I apply more/less? What could possibly let me play downloaded games, leave it half a day playing said games, also after that played both dvd and bluray without any prior incidents, yet as soon as I attempt to play a game shuts down. Summarizing I have a ps that will do anything but play a ps3 game disc. Help this irony is killing me.