Yep, I figured this would be a tough one to resolve.

Maybe I should start by replacing the HD. I've been running the system with just the fans, hd and graphics card connected for a while. Only had one bsod today but sometimes get 3 or 4 in one hour so it's hard to pin down.

Are there any good utils for testing a HD?

Try removing the graphics card and use the onboard graphics and run it like that for a day and see if you still get a BSOD.

If you click the link in my sig then under step 4 you can test your HDD. I dont know of any other ways to test for a bad hard drive.

@stew2 I don't think I have onboard graphics and I've already run the vista disk check. That came back error free.

If you dont have onboard graphics then try using a different graphics card if you can.

You could also try going into the bios and raising the voltage for your cpu to 1.200 V and then test stability.

If you still get BSOD after raising the Volts then i can show you how to underclock your entire system.

Ok, I've run with 1 stick of ram, different graphics card, disabled onboard sound, increased the voltage and still get the blue screen.

Thinking about the best strategy for replacing the MB, CPU and HD.

After doing what you've done the most likely culprit is the motherboard. I see your using the latest bios so the next step is either try it with totally different RAM installed, a different hard drive or just bite the bullet and buy another motherboard.

Yep, bullet bitten, just ordered a Gigabyte GA-EP43-DS3 to replace the Asus. Fingers crossed.

Thanks for the help, I'll let you know how things pan out.