3 1/2 year old i7 system won't boot

I built this computer (my first build) in late 2008 within a week of when i7 was first released with all new components. I use it every day (including yesterday, and didn't notice anything out of the ordinary), turn it off at night, and haven't had any major problems with it until this morning.

System configuration:

ASUS P6T Deluxe motherboard
Intel Core i7 920 CPU
Nexus FLC-3000 CPU Cooler
OCZ 1GB (x3) 1333 RAM
Corsair HX620W PSU
BFG Tech GTX 260 video card
Creative Sound Blaster X-Fi XtremeGamer sound card
2 7200RPM HDDs
1 DVDRW Drive
5 Chassis Fans
Cooler Master Cosmos 1000 Chassis
Windows 7 Professional

This morning after I woke up I turned my computer on, it seemed to turn on normally, and I went to make coffee. When I returned a few minutes later it was off. I pressed the power button again and nothing seemed to happen.

After taking off the side of the case, I noticed that the power and reset buttons on the motherboard were still lit. When I pressed either that power button or the power button on the chassis, the fans would start to spin for a split second, then stop. Thinking maybe one of the memory sticks had gone bad, I tried going down to 2 memory sticks in all combinations in the slots shown in the motherboard manual, with no change.

One thing I noticed is that if I removed the 8 pin PSU cable that goes near the CPU, but left the 24 pin cable connected, the fans would spin up normally. I removed the RAM, graphics and audio cards, unplugged the drive power cables, and tried turning it on with both the 8 and 24 cables connected, and this time it stayed on, but the fans seemed to be spinning slower than normal, especially the fan on the CPU cooler, and after a few seconds it started to smoke from the CPU area.

I quickly shut it down. I removed the CPU cooler and inspected the CPU and motherboard, and I don't see any burn marks or bulging capacitors, or any other sign of damage from when it started to smoke (although boy does it stink). While I guess the absence of obvious damage is a good sign, I am concerned that this fried the CPU (assuming it wasn't before).

This afternoon I bought a multimeter to test the PSU, and every connection on the 24-pin cable and 8-pin cable tested out perfectly. It seemed to me though that the PSU fan was spinning awfully slow, and was almost silent. The PSU mounts on the bottom in my Cosmos case, fan down, so this is the first time I've ever seen the fan spinning, so this could be perfectly normal under minimal load (I did connect a 120mm fan to the PSU while doing the testing as was suggested in a video I found on how to test a PSU with a multimeter). While the PSU checked out with the multimeter, I'm not at all confident that it's putting out enough / correct voltage under load, and I don't know how to test the PSU under load with the multimeter.

Next I put the CPU cooler back on the motherboard, removed the CMOS battery for a minute then put it back, and then tried breadboarding just the motherboard, cpu, and psu. With both the 24 and 8 pin connected, I turned it on and both the power and reset buttons lit up like before. I pressed the power button, and it shut off immediately similar to the first few times I tried to turn it on (although as stated before, the last time I had so few components connected it stayed on and started to smoke). I tried removing the 8 pin cable, and as before the CPU fan came and stayed on at what seemed like full speed, and the ASUS light on the motherboard came on.

So that's where I am now. On various forums today I found several very similar stories (computer begins to start up then immediately shuts down, fans spin up normally with 8 pin disconnected), but none of them had a resolution posted.

I plan on ordering a replacement PSU and/or motherboard early tomorrow morning, so that I can get it as soon as possible. I would greatly appreciate any advice on anything else to try to single out whether just the PSU is bad, or the motherboard and/or CPU is fried. Or if the information is enough to make a diagnosis on what's wrong, that would also be appreciated. If any additional information or clarification is needed about anything just ask and I'll try to answer as quickly as possible.
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  1. The simplest method I can fathom without going through all the rigamarole of playing with a multimeter is to just swap in a known-good PSU.

    Based on your description, it does smell awfully lot like a dead PSU. but I cannot guarantee that.

    If you do not have a known-good PSU, the good news is, your power supply from Corsair has a 5 year warranty, I know from experience they will not hassle you with an Advanced-exchange RMA. They'll ship you a new one fast, but you'll have to give em a credit card number to charge if you don't return the old one within 14 days I believe it is. (You will have to pay the cost of shipping to ship your old one back to them)

    Whether the PSU is the problem or not, I'd go ahead and give em a call and do that.
  2. Another thought, Corsair no longer makes the HX620, if they offer to send you an "equivalent" model try to talk them into giving you a Corsair TX650v2 its not modular like their HX620, but its a very decent PSU.

    Or they might be giving you one of these

    Don't let them try to talk you into a Builder Series (CX models), its not that they're bad.. They're just not really "equivalent".
  3. nekulturny - Thanks for the replies.

    I tried a different PSU tonight, an OCZ Fatal1ty 750W, and had the exact same problem as I did with the Corsair HX620W. With both 24-pin and 8-pin cables plugged in, the power and reset buttons lit up, but it won't start up. After removing the 8-pin cable, pressing power makes all the fans spin at normal speed, and ASUS lights up on the motherboard.

    So I guess that leaves the motherboard and/or CPU. The motherboard is out of warranty. I can get a new LGA 1366 motherboard for about $200, but I'd obviously be screwed if the CPU is fried (from either when it originally shut down or when it briefly started to smoke from the CPU area), which I have no way of testing. If I bought a current Intel CPU (i5, probably), motherboard, and memory, it looks like it would be about $400.

    Suggestions on anything else to try with my system, and also which path of replacement I should take would be greatly appreciated.
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