OK, here it is...
I used my original PSU and took out the graphic card: the problem still here.
I changed the PSU, and without the graphic card: it didn't restart, but there is no visual coming from the motherboard.
I changed the PSU, and I put back the graphic card: it restarted once & twice...
The CPU fan still runs, I just tried to turn the PC just now, it can run for 1 minute before it began restarting (and the processor fan was also running well). Can the 3050 make the computer behave like that? I thought a failing graphic card does is just no visual.
My PC keeps on restarting itself. First, it restarts after few hours, now it keeps on restarting every second. I can't even get to BIOS without it restarting itself. I have done RAM test and checkdisk (before it went downhill), but they were both OK. I have also checked the temperature, it was...