Thanks for reply. I know that PSU is most probable cause, but is it possible because of faulty GPU (its a recent purchase). Also if GPU needs more voltage, will underclocking it help the voltage requirement?
My PSU has 17A on +12v, I thought that it can cope with HD6450, since this card doesn't require that much voltage. Also, the BSODs are increasing, there were no problems for first two days, does this mean that GPU is damaged somehow because of low voltage?