Tom's Hardware: Topic Weird problem: computer won't always power on. Let's troubleshoot!
Tom's Hardware > Forum > Homebuilt Systems > General Homebuilt > Weird problem: computer won't always power on. Let's troubleshoot!
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This is a bit long, so thanks in advance to those who choose to help. It's an odd problem and I just want to give you all the info I have from the get-go. 
First off, my specs:
- Antec Neo HE 550w PSU
- Asus P5B Deluxe WiFi/AP
- Intel Core 2 Duo E6600 @ 2.4GHz
- 2 x 1GB DDR2-800 SDRAM (Corsair XMS2)
- EVGA GeForce 8800GTX
- WD 74GB Raptor HD
- WD 320GB HD
- Pioneer CD/DVD-RW
- WinTV-PVR-150
By the way, nothing is overclocked.
The problem:
Whenever I press the power button on my computer, the power LED flashes for about half a second and I hear some of the fans start to spin up, then stop. It usually doesn't fully power on the first try. To retry, I need to either hold down the power button as if I wanted to do a hard reset, or flick the switch on the PSU off/on. It sometimes takes an upwards of 50 tries to power the machine on. And when it does power on, the machine works perfectly.
Here's what I've done so far in trying to determine the exact cause of the issue:
I have tested the PSU by disconnecting all components except two hard drives and a case fan (as a load). I jump-started the PSU by shorting the green lead to any ground. When I flicked the switch, it turned on immediately. So I suppose it's not a PSU problem.
I have removed all components from the motherboard except the CPU. The PSU has nothing else plugged in other than the motherboard. I hit the power button and the machine turns on and stays on -- it complains on POST that there's no video card (one long beep, two short beeps), but I'm happy that it powers on.
So now I put the video card back in and connect the PCI-E power cables. I try to power the system on and I get the same symptom that I described in the first paragraph: the power LED flashes for a split second and the fans turn on briefly.
So what could be the cause that would cause the computer to turn on occasionally?
Defective video card? I can run graphically intensive programs -- games, mostly -- without problems.
Maybe the slot on the motherboard is faulty? But again, when the computer works, it works flawlessly.
Also, does anybody know of a way to bypass that missing video card POST error? Would it be possible to boot without a video card? This motherboard does not have an onboard graphics chip, unfortunately.
Thanks for reading all of this, guys .
| Paperdoc wrote : Even if you could, how would you know? There would be no way for the system to give you information on what it was doing. |
I was wishing that I could SSH into the machine in case I ever needed to retrieve files off the hard drives. I don't want to buy an enclosure just yet.
| Paperdoc wrote : Can you borrow (or buy a REALLY CHEAP) video card and try the system with that in place? If the problem disappears you'll be confident your original video card is the problem. |
Alright, I guess I'll have to hunt down a video card around here .
"I have tested the PSU by disconnecting all components except two hard drives and a case fan (as a load). I jump-started the PSU by shorting the green lead to any ground. When I flicked the switch, it turned on immediately. So I suppose it's not a PSU problem. "
PSUs are not so simple. Just because a power supply turns on does not mean it provides appropriate power levels in a stable manner.
Just because your motherboard checks for a video card first, does not mean that your video card is bad. Perhaps the next test it performs fails, causing a shutdown. It never gets around to that test when the video card is removed.
My take on this is that the power demand from the GPU at start up causes an unhealthy fluctuation of power from the PSU, causing the system to halt. Eventually with all your button mashing and switch-flipping you get the timing just right where the GPU still has enough power that the new draw does not cause enough fluctuation and so the POST can be completed.
In other words, it's not the amount of power your PSU can produce that is the problem. It's how it responds to sudden loads.
Or it could be the voltage regulation on your motherboard or video card
have you tried using a screwdriver to make the contact between the start pins,,with everything installed,if it works then,you know that the case switch is a bitch,if not then there are three things that can be causing the trouble,psu,cpu,ram,,,, firstly you should try another psu before you do anything else,it is of paramount importance that you are certain of your psu ,,otherwise all else will be a waste of time...
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