Hey so i just had this issue and was able to fix it. I had just taken it apart to replace the thermal paste and when i put it all back together it would start up and function normally but anytime i wanted to start a game the console would freeze like described on OP's post. I tore it back down and it tuned out my disc drive's ribbon cable wasn't fully plugged in causing the issue and once i plugged it back in it worked perfectly again. triple check your cables and if you still are having issues the cable might have been damaged in the process or was going bad.