Well it actually not that simple like you said, I did try those both options above - but seem to no avail.
My first thought was could it be the PSU? but since I just replace the old one, so I highly doubt it.
I even try to unplug some power consuming devices such as (DVD ROM, and CD ROM) but also to no reward. (PSU 350)
Like I mentions above, if I SHUTDOWN my computer right now and power it back on (i can hear the fan goin abit then dead)
The only way I can restore and power the computer back on is to unplug the PSU power cable for at least 1-5 minutes.
I am worried could it be the motherboard or cpu? I'm just out of idea don't know what other task to work on.