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Completely different system here, but the exact same symtoms. The culprit was, of all things, a PC Power and Cooling 510 PSU. I fought the problem for a year, and there were months during that time that it all worked perfectly. But when it didn't it did just what you are experiencing. I finally dropped a Seasonic M12 into the system and haven't had any problem since.Hope this helps,

Greg,Many thanks - very interesting. Did you increase overall power with the M12 or did you stay around the 500 watt mark?John R

Well I use an Antec 480W power supply with similar CPU and peripheral load to you (except no floppyosaurus), and I have no problems at all with booting. I did have such an issue a few years ago when I had a P4 system and the problem turned out to be a common problem with the AUSU P4B motherboard I used. Perhaps ASUS is still being haunted by the dreaded cold boot problem of years gone by? I suggest checking out the ASUS motherboard forums for potential leads.Gary

John, I'm curious, did you use the same brand/type of RAM when you tried swapping it out? Some brands, and also some of the specific models of DDR-800 RAM can cause problems like you are describing. I agree the PSU is also a probable culprit but you might look into a different brand or model of RAM. If you continue with the PSU theory, pay close attention to the way the power is split between the different rail systems of the PSU. Sometimes it is not the overall power of the PSU but that one rail cannot support all the peripherals drawing power from it. I'm afraid my explanation would likely fall short so I can only suggest researching on Toms Hardware Guide or simply Googl'ing it. Of course, someone else here might chip in with a good explanation.

Did you increase overall power with the M12 or did you stay around the 500 watt mark?The PC P&C was 500W and the M12 is 700W. But that means little, really. Using a power calulator I'm no where near 500W (the higher power of the Seasonic does offer me more upgrade latitude, which is nice). And as stated, it would work fine for weeks on end and then be flaky for weeks on end. Was very frustrating.

More power's not going to do it. You have plenty at 550. Actually, I'm running a raid0. plus 2 singles, 2 opticals, 2 gig0ram with an overclocked P4 and an old 6600GT with an Enermax 360 watt PS. Gotta turn it down a bit on warm days, but so far, no smoke. Had a similar problem today on a real airplane. A digital fuel quantity indicator would not power up in a #2 main position. But it worked fine everywhere else. All the other position's indicators worked fine in the "bad" #2 position. Ended up being a connector "personality miss-match" between that specific indicator and that specific cannon plug. With yours, it could be anything (except the "more power" solution!), but it sounds kinda the same to me. Carefully inspect the power connector On ThE MoBo. Then check out the corresponding connectors on the PS. You are looking bent/mashed pins and warbeled-out sockets. It doesn't take much. You can't imagine how many millions of dollars just this kind of intermittent fault has cost airlines. Sometimes it works and sometimes not. The mechanic finally gets a "Checks OK" only to have the next delay follow the last. It can . . . and does . . . go on for years! When you plug the power connectors in, do so PosiTivElY. Don't get too aggressive, but rock 'em back and forth as you are going in and seat them solidly. Do it several times. Get a feel for what "home" feels like. Careful, it's still just a PCB Mobo your pressing on!Same thing with the ram and PCI slots. Look right down in there with your 10 power lope (i.e., Magno-glass. Hey mechs, this is a standard tool item!)Good luck. Persistence is the key. These intermittents can be tough.

Hi John,I have a somewhat similar issue with an ASRock 939Dual-SATA2 mainboard and an Antec NeoHE 430W PSU.Every once in a while I will power on, the fans will run full speed, the HD light will flick on and off every few seconds and the boot will not progress. Up till now, I've waited 30 seconds or so, lost patience and just hit the reset. Boot then restarts and continues normally.More recently, I've just left everything alone and, on those rare occasions when this issue arises, after a minute or two the fans will slow (as they do normally prior to the POST) and the system continues to boot normally.I have now concluded that this is 'normal' behaviour on my setup which is otherwise very stable. I'll start to worry on the day it fails to POST.MikeASRock 939Dual-SATA2, AMD Athlon 64X2 4800+ (2400MHz)(Toledo), 2GB Crucial PC3200 DDR400 Ram 3-3-3-8 (2T)(Dual Channel), (PCI-E)Sapphire ATI Radeon X1950 Pro 512MB (Catalyst 7.1 WHQL), Hyundai ImageQuest Q17 17" TFT LCD 20ms Digital Monitor (1280x1024x32), SB Audigy2 ZS Platinum (Drivers version 5.12.0001.1196 WHQL), WD Caviar SE16 250GB (WD2500KS) SATAII + Hitachi Deskstar T7K500 ATA133 UDMA-6 (320 GB), ASUS DRW-1608P2S Optical Drive, Antec P150 case with NeoHE 430W PSU, Logitech MX1000 Laser Mouse, Windows XP Home Edition (SP2), DirectX 9.0c

After upgrading/building/repairing many hundreds of machines I'v come to see that the PSU is often overlooked by many guy's who upgrade their machines.I have seen many times when a machine came to my shop with the complaint that it would not boot reliably. When I plugged it into my UPS it booted fine every time. If I plugged it into the wall socket, problems. This seemed to me that the PSU was marginal, almost good enough, but not quite. Some times regular electrical grid power may fluctuate enough to cause problems, mini brownouts occur often in the summer time when AC's are in heavy use.Too much power is never a problem, too little can be problematic. A PSU thats right on the line can be worse in a way, confusing!The machines I build now all use a 750 watt PSU or higher, NEVER have problems. Add whatever you want, HD's, CD's, 2xVid cards, no worries.

A few things to comment on as well:Check tomshardware.com There are some good lists there of different 'tiers' for PSU's. All 500W PSU's are not the same.I went with a OCZ GameXtreme PSU.Unsteady voltages, poor effeciency, non-rated power all can be devistating culprits to a PC.If you plan on upgrading your video card anytime in the future I'd suggest getting a 700W minimum. No, you may not use all of it, but it will run cooler because you will be under the max, and if you get a quality PSU, your power supplied to your PC will be much much more stable.A PSU can make or break a PC.

Many thanks to all.After 5 days of testing on the bench, my dealer finally agreed that it was a mobo problem and persuaded his supplier to do a swop out. New P5B-E mobo arrived and installed today and running as advertised.Now I have a problem with Windows XP not recognising more than one IDE optical drive - but perhaps that's for another forum!John Rooum