Power issues...

[rockmand]

*** First off, my PSU was an Antec 380W, which came with my Antec Sonata case.

So, I was toying with the idea of upgrading my GPU. I powered down my PC and unplugged my computer (without turning off my PSU switch) to take a peek inside. After plugging everything back in, I tried powering up, but nothing happened. I tried resetting my PSU with the red button, which did the trick. That was a little weird, but I wasn't too concerned.

So, I went ahead and bought an AGP Radeon x1650 pro 512MB. This time I switched off my PSU after powering down as well as unplugging everything. I switched out my 9800 pro, plugged everything back in, and switched on my power supply. My computer powered up immediately without me pressing the power button for the PC. Again, weird, but not that big of a deal. However, my PC did nothing. It appeared to be powered up, but would not boot up. Not even any motherboard beep patterns for a GPU problem.

Once again, powered down on the PC, turned off my PSU, and unplugged everything so I could put my 9800 pro back in. This time no power at all. So, I reset my PSU again with the red button. Sure enough, my PC powered up once I turned on the PSU, and began to boot up fine.

So, I tried my x1650 pro again, but I had forgotten to unplug my PSU or switch it off, which I did not realize until my PC powered up out of nowhere. I figured everything was fine since I had just finished plugging the x1650 pro before it turned on, but a small puff of black smoke came out of my case right in my face. It appeared to originate from my CPU fan, but the CPU shows no scorch marks, nor could I discover any on my motherboard. I couldn't find any popped capacitors either.

I've tried troubleshooting my PC, and it appears that the only piece of hardware fried is my motherboard (AMI bios 4 beeps = system timer failure). I even purchased an Enermax 420W PSU to be safe, which also turns on my PC immediately once I turn on the PSU power button.

I don't think my 380W wasn't enough to power up one optical device, one HD, and one GPU. So, is this normal behaviour for my PC to power on without power on the PC directly? I honestly can't remember, but I don't think it used to do this. Could I have a defective power switch on my case? I'd like to pin-point this problem because I am buying a new mobo, CPU, GPU, and RAM, and I'd rather this scenario didn't re-occur.

 

[mpilchfamily]

Try dissconecting the power switch from the motherboard then plug everything back in. If it still powers on by itself the the motherboard is the problem not the switch. If the PSU was too small it could have damadged the motherboard. Keep in mind its not the total wattage of the PSU but how many amps it offers on the combined +12v rails.

 

[Uppsala9496]

I've got a similar problem.

I have an old NF325-A7 board (old cpu, but the board was a newegg open box from March 07).

I went to add a wireless networking card yesterday and was having some serious issues with Ubuntu. So, I decided to toss in a larger HD that I had sitting around.

Point is that as soon as i plug in the cord to the power source, the mobo starts running. All of the fans start, along with the power light on the front of the case.
I've unplugged everything, cleared the CMOS, removed and replaced the battery. Still no luck. I get power going to the mobo, but it won't post (power switch on the front won't turn it off either).
The only way to turn it off is to hit the power switch on the power source.

Is it the motherboard that suddenly died on me, or something else?
Even if I remove the 4 pin 12v cable, the same thing happens.