check if your motherboard needs any additional power cables plugged in other than the main cable like a 4 pin connector
That 4-pin CPU connector would cost it to reboot every 2 second OR you can said 'No Boot"
Cheap PSU dont just cause the system to shutdown IF there's no problem to it... The PSU is faulty or in a bad situation... If it's a Good PSU Like Corsair's PSU and cause shutdown, it's a faulty one OR one of your System part is overheating... Check your Temps in BIOS instead of in OS because OS/Software is off by 2-20*C