Why does my PS3 shut down trying to boot more complex games?

I haven't used my PS3 fat for a couple of years. Now to start it I have to try five or six times to enter safe mode, then select any option and it will start. I can play blue ray movies and some simple games. if I turn it off then turn back on in less than about 30 min it starts. If I try to play a more complex game it shuts down shortly after the intro. I replaced the hard drive -- no change. Help??

Your Fat PS3 might be starting to show pre-Yellow Light Of Death problems.

Near the Cell CPU of the PS3, there are some capacitors that the console uses to store small amounts of energy for the processor to stay stable under very heavy loads. The fact that you mention that the console turns on with complex/heavy game also helps with my theory.

The YLOD or Yellow Light Of Death happens because Sony used really low quality capacitors on the Fat units and the first Slim unit (CECH-20XX).

Your only option is to go to a repair shop and request a YLOD fix or change this capacitors yourself (there is this well known guide for replacing the capacitors on PSX-Place).

I'm 100% sure that is not the CMOS battery, due to only being used to store the time when the console is powered off. You can even start a PS3 without a CMOS battery and it will work.