If you've been happy with the 8800GTX, the considerably stronger GTX460 may be all you need to spend on a GPU, but especially if it is four years old, you should replace your Rosewill PSU. The old ones weren't that great (although a few actually passed jonnyguru's testing), and yours may have helped your GPU to die.
A quality modern PSU has full range active PFC (no little voltage switch) and at least 80+ certification. Something like a 550W Antec Truepower New would do well for you.
If you decide to build an entirely new PC, please follw WR2's link and post your answers.