twajetmech

I doubt either one of those pre built computers have a psu capable of powering your videocard, please look on the psu's of each machine and list their specs. Its quite possible that with the addition of the videocard you overstressed the psu and caused the failures. Since changing the graphics card did not solve your problem I don't think you can blame this on Nvidia, most pre-built systems come with really craptacular psu's...espeecially those in the price ranges of the listed machines (mid to low end) despite the fact its states in the case of the second machine its 600W....if you read our psu artical (linked below my sig) you'll understand wattage is not all what its cracked up to be. I would think that a simple psu replcement with a good quality psu's (use the artical's psu selector and add 30% to the results for a psu reccomendation) will bring both computers back to good use. I would also reccomend using either the latest drivers for the card or using the well known and stable 84.21 driver to rule out any potential issues with a bad driver (be sure to remove the old driver before installing any new ones) I would expect to see a good 750W psu from the likes of Antec(Trio), Seasonic, OCZ or PC Power & Cooling for your machines