Ok, it was a last week that my computer was down suddenly.

I was trying to reboot it, but after Dell logo came up on screen, it la down again.

Waited a few minuets, it's back on for 3 mins and down again.

After that, it acts like crazy, turns on and off be itself a few times.

I had to unplug the power cord from power unit to completely off.

No beep sound. It's just down itself.

I had extra power unit, tried but same issues.

I had extra hdd, tried but same issue.

I had extra motherboard, same issue.

What else could be the problem?