If the computer is restarting, a better PS would be a good place to start. My experience is that the 5V signal has the least "margin" on most power supplies but even my Athlon 1.33 system which has a 300 watt Enermax supply never dips below 4.95V. In contrast to what many will tell you, a 300 watt supply is adequate if it's a quality PS. However, no name 400 watt PS might not be enough for an Athlon system.