My computer is one that I put together myself so when it breaks I am the only person arround to fix it. The other night the computer turned off and the PSU started smoking. I hoped that all I needed to do was replace the PSU. Unfortunately it wasn't. When I switch on the PSU the lights on my case flicker on for a brief moment and then go right back off. The green light on my mobo is on but when I push the power button on my case nothing happens at all.

What all could be broken and need fixing?

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Are we talking about brand new PSU?
If the PSU is OK than it leaves you with either mobo or CPU. (or both)
I does sound like PSU is not working properly, or it has protection that shuts it down if shorted, and that can be reseted only by unplugging the mains cable. In such case, my advice is to strip your machine down to the PSU, mobo and CPU only. (No memory, peripherals, VGA, PCI cards...) If it comes back to life, start replugging one thing at the time, until you figure out which one is shorted.

If the PSU-mobo-CPU combination gives you the same symptoms (dead mobo or CPU), only thing left for you to do is to unplug the CPU and see what happens then. Mobo without CPU should (not necessarily) give you the beeps, if you have a beeper. That would mean (again, not necessarily) that the CPU is toasted, and not motherboard.

Yes, it's a brand new PSU. I bought it yesterday to replace the smoking one. It's a 680W Aspire PSU. I'll try taking everything off and see if the MoBo/CPU work alone. My case also requires me to plug in a 12V to it... Could that cause issues?

I unplugged everything. The fans turned on when I turned on the PSU. But I couldn't turn it off by pushing the off button on the case. I plugged the video card back in and it seemed to work. The fan on it turned on and the monitor turned on. Right after the monitor came on it went into off mode. Again the power button on the case didn't do anything. So I kept connecting things slowly and the computer kept working until I plugged in one of my RAID Harddrives. When I plugged that on it and turned it on it started to smoke and the computer turned off. Now I'm nervous to plug the other HDD that's part of the RAID back in.... I do still have my IDE HDD which seems to be working.

So now I am wondering why did the SATA HDD start to smoke?
Why doesn't the power (or reset) buttons on the case do anything?
Why doesn't anything display on the screen when I turn it on?

If the SATA drive shorted, it most probbably fryed the first PSU. New PSU dettected the shorting and protection kicked in.
Now, in this situation, the beeper would come in handy.

From the looks of it, seems like your motherboard is fryed by either fryed PSU or shorted SATA drive. That would explain graphic card and the off button not working.

I suggest that you use the warranty on the HD and mobo. If they ask you what happened, just say "it was working fine, now it won't work". Keep these details to yourself, 'cos they might refuse your warranty if they suspect that faulty HD fryed it.

Graphic card could be next in line, but that doesn't have to be.

Is 2nd SATA working fine?
Did you try reseating the graphic card?

commented: Very helpful +1

I didn't dare plug the other SATA HDD in last night. The smoke made me a little scared. ;)

And no, I haven't tried reseating my video card.

Is there a chance that the Mobo is fine? And the CPU and Video card are the problem? Or are we pretty certain that the Mobo is toast?

If you were wondering, my Mobo is an ASUS K8N-SLI Premium

Anything could be fried there. My prime suspect is mobo, but CPU isn't excluded. For CPU to get toasted, PSU has to over-voltage "core voltage". That has nothing to do with HD whatsoever. For the mobo, any of the voltages can fry her. Remember, all of the wires (except 12V and 5V) go trough the motherboard.

There is no way to be certain what is fried and what survived, except testing the parts on known good system. If you replace the motherboard with new one, that would be a start. From there you will see if the CPU and VGA survived.

Don't forget to replace the HD first.

Because of the on/off issue I'm inclined to agree with Chaky that the motherboard is at fault.

The obvious first choice is a mistake made. Go back to MB, PS, one memory module, floppy drv, & W98, DOS, or other bootable floppy. If it works, shut down, add component, reboot. Don't add HDD till the end. This is rare for MB failure, but it happens w eMachines all the time, so why not you. Look for errors you made (we all make 'em). HDD symptom extremely rare. Check cables, bent pins, connectors again. Try one of those wonderful, cheap power supply testers from CompUSA or Frys for $10. If it doesn't work w/ floppy boot, I'll bet on bad board... not the drive.

I'll bet on bad board... not the drive.

The drive went up in smoke. Can't get more obvious than that.

But the reason it went up in smoke was not the drive failure, but the board failure.

It is connected to the board via SATA cable. Not power cable. And earlier PSU went up in smoke too.

Well I replaced the Mobo and it seemed to fix the problem, until it have me a CMOS Checksum error right have the BIOS screen.

Wow I made no sence in that last post... so here I try again.
Well I replaced the Mobo and it seemed to fix the problem, until it gave me a CMOS Checksum error right at the BIOS screen.

There is a jumper (usually near the CMOS battery) that clears the CMOS. Switch the jumper and wait about 10 seconds, then switch it back. That should take care of the checksum error. You might need a BIOS upgrade.

I cleared the CMOS and rebooted and it gave me the samme error again. On the screen it gives me two options "F8 continue" or "Del - Enter Set up". no matter what I press on my keyboard nothing happens. :(

Okay, I discovered my keyboard is bad. One problem solved. My CMOS isnt giving me any problems now. Rather, when I reconnected my HDD it loaded Windows increadibly slowly. So I decided to reinstall Windows. When I booted from the CD it went very slow doing that. Then when I tried to reformat my HDD the installation failed and I had to restart. So I tried again. This time it got to 50% before it failed. Is my HDD bad or is my CPU pooping out? Or is it both?

I never could understand why the manufacturers never suggest clearing the CMOS after installing a new motherboard as standard procedure, you wind up having to do it most of the time anyway.

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