multiple problems on build computer

Hi everyone, My friend decided to build a computer so i helped him out what on what he should get because i believe have some pretty good knowledge on that. he received everything and build up his computer himself. now he has multiple problems on it . First the processor was overclock and was giving him an error. He got that part fixed. now he claims that when he boots up the computer for the first time it turns on for about 2 or 3 seconds turns back off automatically and then turns back on and boots up normally again. Once the computer has been up for like an hour it shuts off by itself. i told him to make sure that it was not in stand by and to check all his settings. he claims that he has all the settings correct and even put on his harddrive so it will never log off. does any one have any clue on how to fix these two problems that have occured?

Did he use TIM - thermal interface material - between the CPU and heatsink fan (HSF) assembly? Some form of TIM MUST be used. Typically, the thermal pad that comes with stock HSFs is adequate. But if it was previously used or missing, a fresh layer of TIM MUST be applied.

What is the CPU temperature?

If he is overclocking, don't.

Is the PSU adequate? Use the eXtreme PSU Calculator Lite to determine your power supply requirements. Be sure to read and heed the notes at the bottom. I recommend you set Capacitor Aging to 30% and if participating in distributive computing projects, I recommend setting TDP to 100%. I recommend using brands listed under the "Good" column of PC Mechanic's PSU Reference List. Attempting to save a few dollars by getting a cheap supply is a mistake. Digital electronics needs clean, stable power. A good, well chosen supply will provide years of service and upgrade wiggle room.

Is there adequate front to back air flow through the case? Are all fans spinning?

If the CPU fan speed is being controlled automatically, disable that feature in the BIOS.

Run Windows Memory Diagnostic or MemTest86+ to test the RAM.