Problems with PC

Formatted it 3 days ago, was running fine until today, it was registering 8gb ram instead of 16gb so i opened it up and cleaned all the dust with some duster.

Plugged it all back in and it wouldn't boot, reset CMOS and it still wouldn't boot. I removed heatsync cleaned dust from it and attached it back, pc is running fine. I start a game up CPU goes to 89 Degrees and does a force shut down. Any idea what I can do ?

reapply the cPU
happens to me, might be an opening or something

Apply new thermal paste, check the heat sync is attached correctly.

As others have said; reapply thermal paste to the CPU. Although ensure the cpu fan is fully operational aswell as adequate airflow is present through the case. If this still doesn't work go into the BIOS and select CPU settings, here you'll be be able (in most cases) to adjust the voltage. Research what voltage is required for your cpu then set it to the minimum as lower voltage = lower temp.

Hope this helps

ALT ++ F4ALT ++ F4

checked the thermal paste? changed for a long time?