Hey tomshardware community, I'm in need of some dire help. A little while back, about 4 weeks or so, my computer crashed, and wouldn't boot up or post BIOS at all, I tested some parts, sent out the mobo for repair, it came back and everything worked well for about 5 days or so.
Now, I'm having similar, but not exactly the same problems. Let me tell you what I've done to diagnose my problem.
1. I've tested the PSU with a PSU tester and all lines are giving out a voltage within their respective tolerances.
2. Reset the CMOS battery.
3. I've taken the motherboard out of the case, taken off the memory, bootable drive, DVD drive, and GPU, put it on an anti-static surface, and plugged in the 24 pin mother board power, and the 8 pin CPU power, and jump started it. The fans on the PSU, the fan on the HSF all spin, and the mobo beeps at me telling me it needs memory. This usually works the 1st time.
Issue: While I'm putting in parts 1 piece at a time, the computer will decide to not turn on. For example, in between RAM stick 1 and 2 it won't turn on, meaning that the little green LED on my mobo labbled "SB_PWR" will light up, but the PSU fan and HSF will not spin nor will any other regular LEDs go on. If I go back to 1 stick of RAM it still won't turn on. If I go back to just HSF and CPU it won't turn on. If I wait an hour and try again, it will most times turn on, and then not boot after I put my GPU into the PCIe slot. So it fails at random stages, but the PSU checks out. Since it at least turns on, it's safe to say that the CPU isn't entirely dead, but maybe damage (i.e. bad die(s)) or the mobo is still damaged.
What do the experts say?
CPU: core i5 750
GPU: GTX 470
RAM: (2x2) 4GB of 1600Mhz G.Skillz Ripjaw
Motherboard: ASUS P7P55D PRO
PSU: Corsair 750TX
It still sounds to me like either the PSU is not putting enough amps out or that the motherboard is failing. I would recommend the paper clip trick to see if you can power all your components except for the motherboard since that could determine if it is the motherboard or the PSU. I don't have the link at hand but a google search will find it.
Sounds to me like something is preventing the power to continue throughout the computer i.e. short circuit. Although the psu checks out fine, try to find someone with compatible parts to swap each individual part to confirm each component functions correctly.
@Enigma One of the very first things I did was the paper clip trick, but that only establishes that the unit has current running through it, not that it's supplying the right voltage to the motherboard, which is why I used a PSU Tester.
@Pocketdexter Easier said than done, motherboard tend to be picky about what kind of hardware they like.
The problem with those little PSU testers is that they put only a minimal load on the PSU. I have one and it is very useful. It can certainly tell you if a PSU is bad, but it cannot tell you for certain if a PSU is good.
The Corsair TX750 is a pretty good unit (I have one of those too ), but it really sounds like you have a PSU problem. The key is "If I wait an hour and try again ...". It sounds like you have problem with the circuits that control the PSU startup.
Original question: "Diagnosis of a Bad CPU". Your CPU is probably OK. You get "bad memory" beeps. But the only way to know for sure is to replace it with a known good CPU.