Previous message wasn't as specific, I don't think you have to get another mobo that is a 915 chipset, as long as the motherboard is the same processor socket as your P4, and as long as your mobo says it supports your processor, then you could get one, ex: 965, 975, etc. You could even get a nforce 4 intel version mobo, I think they work with your processor, but I'm not exactly sure, but most likely. Take the mobo you have to a third party instead of relying on the "Geek squad" since most likely they're just spewing BS since its the easiest diagnoses just to tell you that its fried, and you'll have to buy a new one (from them) and have them install it for you. Take it to a computer repair shop, ie: a local mom and pop computer shop that'll most likely have someone that is a certified computer technician, instead of a bunch of high schoolers diagnosing computer problems.
Oh and don't shop at Best Buy, everything they have is overpriced, $22 round ide cables (wtf?), $30 computer tool kit (only option to get the antistatic wrist wrap is to get the toolkit). Just get stuff like Windows XP if you made the mistake not to get the oem off newegg (don't make that mistake!).
C2D E6600 @ 3.15ghz w/ 1.35 vcore
2GB G.Skill DDR2-800 (4-4-4-12)
XFX 7600GT xXx