first of just to make sure the psu is handling your system , please remeasure the voltages with the multimeter and report back
try these:
while the pc is off ground yourself by touching one of the case sides, disconnect the power cables from everything the floppy/hard drives/optical drives/case fans etc. also disconnect the main atx connector and then reconnect it all and see how it goes , also make sure the graphic card is sitting tight also that the cable between the graphic card to the monitor aint loose , if that didnt work then if you got more then 1 stick of ram try each one seperatly (disconnect 1 of em and if still will be same then reconnect it and then disconnect the other) , if those didnt help then its gotta be the graphic card or mobo , test the graphic card on a friend's pc or another pc if you got one
try these:
while the pc is off ground yourself by touching one of the case sides, disconnect the power cables from everything the floppy/hard drives/optical drives/case fans etc. also disconnect the main atx connector and then reconnect it all and see how it goes , also make sure the graphic card is sitting tight also that the cable between the graphic card to the monitor aint loose , if that didnt work then if you got more then 1 stick of ram try each one seperatly (disconnect 1 of em and if still will be same then reconnect it and then disconnect the other) , if those didnt help then its gotta be the graphic card or mobo , test the graphic card on a friend's pc or another pc if you got one