|A defective power supply can reset at any point, regardless of how much you "lighten the load" as it would generate poor quality power. To confirm it's not your hard drive, try disconnecting it altogether and if it still reboots, you've narrowed it down more.|
Bad RAM will also cause reboots and your 3-second test run on powerup is pretty much 99% inaccurate. If you have more than one stick installed, take one out and try booting with that. If one doesn't work, swap with another.