Need a new mobo and processor....What's compatible?

I have an ASUS a7n8xe-deluxe that I think is dead. I replaced the power supply and I get the computer to turn on but nothing on the screen. Plus, slowly the lights on the back for the internet activity have stopped showing up when psu is on probably indicating the motherboard is done, especially since all the fans, drives, etc turn on.

I would like a pretty decent mobo and processor for gaming and was wondering what would be compatible with my case given the ASUS I currently have. I'm kind of new at building (had a friend help me with the current one) but would like to replace as little as possible (my HDs are fine, dvd-roms are fine, vid card is not pci-express but hopefully I can still use it on a new good mobo).

Any suggestions? I've been scouring newegg but just don't know which ones will work with what I have.

around $350. Although, with a new vid card I may have to up it somewhat. I doubt I could go higher than $400. (Although I could pawn my old vid card for a little extra $$$).

Wow, g-paw! Awesome job. Thanks a lot! Definitely doable for me!

I'm currently using an ATI Radeon x1600 Pro 512mb AGP. Will I still get the same performance for gaming from the 8600GT card you listed?