The PSU probably did a number on your old system when it died although not completely destroying it, but enough to permanently mess something up.
This is the reason why I always recommend people to shell out the extra cash for a quality brand like Seasonic or Corsair as opposed to a cheap PSU of questionable quality. You pay the premium not for how much power it can provide, but for its reliability, and in the case of a failure, the safety measures it has in.
If you get a new GPU, of the two go with the GTX 460. If you have to get the 480, consider dual 460s in SLI instead. It performs much better than the 480 alone and is much cheaper as well. Also the HD 6850 that just came out is comparable to the 460 and more HD 69xx are to be release later this month. Just something to consider.
If your MB clock needs to be reset all the time, it might be time to replace the coin battery.