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Build Repeatedly Shuts Down, Monitor Blank

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October 12, 2009 5:06:49 PM

I've had this rig for a good 8 months now and it's run flawlessly, up until last night.

It locked up, repeating sound, blah blah, and when I shut it down in the normal manner, it proceeded to turn itself back on, or try to anyways. The monitor remained blank, and about 10 seconds after it turned back on, or would shut back off and repeat the process, sometimes taking less than 5 seconds to shut down again, or 15+, at which point I flipped off the PSU as it was the only way to stop this process.

Also, the CPU heatsink fan will not spin up. I'm using a Gigabyte EP45-UD3P mobo, so it usually hangs for around 10-15 seconds before it kicks in, but it just would not start.

I'm going to guess the issue is mobo related, but this is my first serious issue with any hardware, so I really can't say. Everything else powers on absolutely fine. GPU fan goes, all case fans get going. Everything seems to be in order, but it just won't boot at all, and I'm not willing to try and let it run its course without the CPU fan running.

Haven't had a chance to try much troubleshooting because it's the only computer in the house, and I'm not comfortable mucking around with stuff I'm not sure about.

Here's the innards if it's needed.

Gigabyte EP45-UD3P Motherboard
Core2Duo E8400 @ 3.6GHz
4gig mushkin DDR2 RAM
Corsair 650TX 650W PSU
Xigmatek HDT-S1283 CPU Cooler
WD Caviar Black 640g HD
Vista x64
a b B Homebuilt system
October 14, 2009 2:14:16 PM

The cause VERY likely is rooted in the non-functioning CPU cooler. When it does not work, two things can shut you down quickly. One is that the CPU itself heats up rapidly; the mobo BIOS monitors the temperature sensor inside the CPU, sees it shoot up, and shuts down right away for protection. Some mobos also have a second method. They monitor the CPU cooler's fan speed and, if there is none, they shut down even without any fast temperature rise.

Now, you can try for the easy fixes first.
1. Check the fan itself. Is there anything stuck in it, preventing it from turning? Turn the fan by finger - does it turn easily and smoothly? If you spin it, does it coast down slowly or stop really quickly? Probably the most likely trouble is that fan itself has failed, often from seized bearings. If that's the case, replace it.
2. If you think the fan is OK, try just unplugging it from the mobo connector and re-plugging, a couple of times. IF the contacts in the connector are just dirty, this will clean them enough to get it going again.
3. Even if your inspection above says the fan looks OK, get another one and plug it into the mobo. Connect power to the machine and turn on, watching the new fan. The machine may well shut itself off again in 5-10 seconds as the CPU heats up with no fan. Even if it does not shut itself off, YOU should turn off after no more than 5 seconds to protect the CPU. Now, did the new fan work? If yes, you have just proven your mobo fan supply is just fine, and the old fan is faulty, so replace.
4. OK, now we're down to where you thought you were - maybe the mobo is faulty and cannot power the CPU fan. If that is the only thing wrong, there is a work-around. You need a small adapter that will plug into an empty Molex power connector from the PSU - those are the ones with four holes in a straight line, usually plugged into the back of an IDE drive to supply power. The other end of the adapter just has pins to allow you to connect your CPU fan. When you connect your CPU fan via adapter to the Molex power connector, the fan will run full speed all the time, but it will cool your CPU. However, when you do this, you must go into the BIOS Setup screens (usually by holding down the "Del" key as the machine is first booting up) and find the place where CPU and case fan cooling is set up. Go to the CPU fan area and set it to IGNORE the CPU fan speed. If you don't plug that fan into the mobo (you just plugged it into a Molex connector), the mobo will get no speed signal and believe that fan is not working - it MAY shut you down, or at least put out a loud alarm! The Ignore setting prevents this.
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