When I turn the computer On it reset itself after a while (about 30 minutes). After that it runs normaly. I have reinstal windows several times so it is not software fault. Any idea where the problem is?
Just a shot in the dark but check your power management settings in BIOS. Make sure it's not set to turn on by a device. Also check your main powewr connection to M/B from power supply and check your power cord into power supply to make sure it's seated well.
