I've been running my ASUS P6T Core i7 System since May, and it has run well. When I attempted to boot it today, it would not post. The power would come up, the bios would start to load, and the system would shut down, then start up again. It did this over and over, then eventually stopped on its own. Sometimes there is a long delay between the attempts to reboot. Sometimes there is a single beep before it attempts to reboot. I reseated everything (CPU, Heat Sink, Memory, Video Card), reset the CMOS (by removing the battery), tested each memory separately, and did the usual checklist testing. It continues to start to boot, then shut down, start to boot, shut down. Sometimes it makes it to Express Gate flash screen (but not into express gate) before restarting, but most of the time it doesn't get that far. I'm thinking the motherboard is the problem because if it was processor or RAM, it would NOT do a partial post before restarting. I'm not overclocking, I have not added any software or hardware lately, and the casehas not been moved to make me suspect a short. It worked perfectly until this evening's symptoms. I've read all the ASUS P6T postings I could find. Anyone have any ideas?
Here's my system:
Intel Core i7 920
ASUS P6T Motherboard
3x2GB Corsair DDR3 Memory
Coolmaster V8 CPU Cooler
EVGA GTX 260 Graphics Card
Antec Earthwatts 650W Power Supply
Powerspec C5 ATX Chasis
WD 7200 RPM 400GB HD
Windows 7 RC 2100
Try to verify (as well as you can) that the PSU works. If you have a multimeter, you can do a rough checkout of a PSU using the "paper clip trick". You plug the bare PSU into the wall. Insert a paper clip into the green wire pin and one of the black wire pins beside it. That's how the case power switch works. It applies a ground to the green wire. Turn on the PSU and the fan should spin up. If it doesn't, the PSU is dead.
If you have a multimeter, you can check all the outputs. Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the 5 volt standby.
The gray wire is really important. It sends a control signal called something like "PowerOK" from the PSU to the motherboard. It should go from 0 volts to about 5 volts within a half second of pressing the case power switch. If you do not have this signal, your computer will not boot. The tolerances should be +/- 5%. If not, the PSU is bad.
Unfortunately (yes, there's a "gotcha"), passing all the above does not mean that the PSU is good. It's not being tested under any kind of load. But if the fan doesn't turn on, the PSU is dead.
On to the real troubleshooting ...
Disconnect everything from the motherboard except the CPU and HSF, the two power cables going to the motherboard,and case power switch. Boot. You should hear a series of long single beeps indicating missing memory. Silence here indicates, in probable order, a bad PSU, motherboard, or CPU.
To eliminate the possiblility of a bad installation where something is shorting and shutting down the PSU, you will need to pull the motherboard out of the case and reassemble the components on an insulated surface. This is called "breadboarding" - from the 1920's homebrew radio days. I always breadboard a new or recycled build. It lets me test components before I go through the trouble of installing them in a case.
If you get the long beeps, add a stick of RAM. Boot. The beep pattern should change to one long and two or three short beeps. Silence indicates that the RAM is shorting out the PSU (very rare). Long single beeps indicates that the BIOS does not recognize the presence of the RAM.
If you get the one long and two or three short beeps, test the rest of the RAM. If good, install the video card and any needed power cables and plug in the monitor. If the video card is good, the system should successfully POST (one short beep, usually) and you will see the boot screen and messages.
Note - an inadequate PSU will cause a failure here or any step later.
Note - you do not need drives or a keyboard to successfully POST (generally a single short beep).
JSU - I have an identical PSU that I can swap out and see if that fixes the problem. Thanks for the paperclip trick and breadboard link (more like waterboarding, if you ask me). Kufan64, thanks for the link. I had not found your thread with my search, but it does look similar. It may take me a few days to run through the suggestions, but I will post what I find.
make sure you have your ram inseted in the correct slots - for that paticular motherboard you want the orange slots (closest to cpu - 2nd, 4th and 6th slots) - there the oppisite way arround (this is listed in the manual)
also try booting with 1 stick of ram in the first orage slot
oh and corsair and ASUS sometimes has funny issues so try just the one stick of ram and get into the bios and manally configure everything - memory voltage, ratio etc - set the ram down to 800mhz to try.
Thanks for the suggestions. I replaced the PSU, but that didn't help. I breadboarded my system, then connected only the Motherboard, CPU, HSF, PSU, and one stick of RAM in the correct slot. The reboot cycle continued. I tried different RAM configurations without improvement. Almost all configuratons produced a single, short beep and initialization before shut down and restart.
It seems my motherboard has failed (like it did for Kufan64). Since I'm still under warranty, I will replace it and post the result.