|"If its unpluged and it works fine and i plug in the fan it freezes after 5 minutes. WHY ?"|
It's not working fine without the fan. It's getting too hot. You need the fan to blow the heat away. Are you sure the fan is connected to the proper header on the board? Have you monitored the CPU temp in the BIOS, with & without the fan connected? Who installed the heatsink? Was it installed correctly & with the proper amount of thermal paste?
"I tried to clear CMOS, but still no solving this problem"
Why would you do that? You have gone into the BIOS & reconfigured all the settings again? (not just date/time)?