amd:asus:matrix:7970

Hi guys. I bought MATRIX-HD7970-P-3GD5 and it worked for some time but then i tried underclock and undervoltage (because PC was shutting down during furmark stresstest due to weak PSU 400W) the card using GPUTweak2 (from asus site). PC run for longer but it again shut down and then it didnt...