PSU or GPU issue?

Jan 9, 2015
My system was running fine with below specs

  • Core2Duo 2.66 GHz on Digilite G41
    6GB DDR3
    250 GB SATA
    Zotac GTX 650 Ti
    Frontech 450W PSU
    Win 7 Ultimate 64

My HDD crashed and I replaced it with a 1TB SATA. Since then my system goes unbelievably slow when I install the NVidia graphics driver, freezes up every 2 minutes and keeps me waiting for the next 5 minutes.
If I unmount the GPU, uninstall driver and go back to motherboard VGA port, then system is all good again.
Though there is no distortion in graphics ever, even in games (except they run ridiculously slow), so don't think the GPU has gone faulty.

Is the PSU unable to power the GPU and an 1 TB HDD together? I disconnected the 2 chasis fans but no effect either