PC starts up but shuts down after awhile

Hello,
So I am not sure the exact specs of my PC but it’s a low end gaming rig that has got some problems, that never caused problems. Has a 6 core prossesor with the 6th core unstable so it’ is set to only run on 5. But the only problem I have had with it is that recently, couple years ago, when I finaly started it back up to play my MMO (had not used it in a long time, maybe 6-9 months?) it started up fine and I logged in and opened my game up and then the audio and video died. Thought maybe it crashed or needed an update since it had been so long. So I had to hold the power button down, set my power button to sleep the PC, and then started it up again. Got past the log in, went to setting to check updates and it said it was good for that then it lost audio and video again. Turned it off and on and I logged in then it died. Then it would get to the log in screen and die again. If I left it for an hour or so it would let me use it for 15-20 mins before doing the same thing.
I read in another forum on another cite that it could be capacitors that swelled from moisture and that is why it works for less time, heats up and expands, breaking the connection and thus shorter time before it cuts out. I took a cursory glance inside the case but I am more software than hardware but it looked like the RAM was seated right and heat sink was fine and not terribly dusty. The tower had been in the trunk of my car for several weeks (do not drive much) and my house used to be really humid before central air.
I saw similear but not the same problem posts here and around, any further ideas?