I built my system a couple of years ago with a Asus A7N8X Deluxe mobo and Athlon 3200XP, but the other day it just stopped booting and wouldn't power-up. I've tried swapping out *everything* (mobo, PSU, CPU), but I'm still getting the same problem.
If I don't install the CPU then the talking motherboard tells me "No CPU installed", but when I install the CPU it just powers-up for about 5 secs then dies again, without so much as a POST beep.
Please help, it's driving me nuts!
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I think at this point you need to find another cpu to test.