motherboard - Computer restarting, no error messages. Could this be a faulty/incompatible part of the computer?

Last summer I bought a broken power supply (without knowing of course) and put it in my computer. Turning my box on made one of my cheaper HDDs catch fire (I believe a capacitor or resistor blew) and I thought I completely killed my system.

My other 4 hard drives survived the surge (Western Digitals, better quality is why I guess they were spared). And I never had any problems with my motherboard/RAM/CPU because of it. I bought a new power supply and left it behind me.

In the past couple months my computer has been randomly crashing for no apparent reason. I'm never able to recreate the crash, as I can never tell when it's going to happen (it doesn't even seem to have anything to do with intense usage). The process goes as follows:

• The computer fully turns off. Just dies. However, the little light on my motherboard telling me my power supply is on, is still on.

• Pressing the power button on my computer doesn't have any effect here. To restart I have to manually turn off the killswitch of my power supply. When I do this, the light on my motherboard goes off and my subwoffer makes a sound. Then it comes back on for a second (accompanied by another subwoffer noise). Then it turns off.

• Turning the killswitch back on, I can reboot and hope it doesn't happen again.

At first I thought overheating (I was running at high Vcore and my CPU temperature was high). I turned on the "Cool n' Quiet" function of my motherboard, and I still got a crash.

Next thing, obviously, is power supply. However, I was wondering if the initial broken power supply I bought damaged my motherboard or something like that. Which could explain why a power supply that was bought from a trusted store and brand new is seemingly "failing".

So basically what should I do? Replace my power supply again? What if the motherboard is breaking my power supply (if that's even possible)? Should I just spend 500$ on a new motherboard + power supply?

EDIT: I've noticed that it crashes mostly when I'm watching a YouTube video or watching an HD movie in VLC. It's odd because a software pattern is seemingly effecting hardware :(

EDIT 2: I now believe this might be a CPU overheating issue. Someone please tell me if CPU overheating could cause what I'm about to explain. I ran Clementine (music player) with full screen visualizations enabled on fast mode. While I was doing this, I was watching the CPU temp go up and up. It finally capped at around 81C, at which point I opened a browser to see how 'hot' that was. The crash happened. Is this definite proof that I'm dealing with an overheating issue?

EDIT 3: My CPU is AMD Athlon(tm) 64 X2 Dual Core Processor 6000+ rated at 3.1GHz (or something around that frequency). I'm not over-clocking at all.

FINAL EDIT: I'm happy to announce that I've solved it with the help of you guys. I bought some artic silver thermal paste for about 8$ and applied it to the CPU/HeatSink. Along with a good de-dusting and some better cable management, my computer is running at a cool 35C idle. Thanks to everyone who helped.

What you described to me looks like some sort of safety system in the power supply.

I recommend that you disassemble whole computer and check for any burn marks on the motherboard and pretty much everything else. There could be something which causes a short and makes power supply turn off. Pay close attention to computer case and check if it's moving or vibrating.

Next step would be to check cables in your power supply. If you have multi-rail power supply, you could be hitting rail limit for power. Make sure that load is distributed among cables and devices. If a cable has several connectors on it, try to use up all other cables first before using extra connectors. Make sure that you balance load on cables with several connectors. For example on a cable going into a hard drive make sure you only connect low power consumers and so on. This in general shouldn't be a problem, but some power supplies can be picky and may have bad load distribution.

Next check how different devices are mounted. I once had a similar problem. I bought a new computer and every once in a while it would shut down unexpectedly. In the end it turned out that the incompetent or malicious manufacturer used too long screw on the floppy drive. They penetrated inside and caused shorts from time to time. Make sure that nothing similar is happening in your case.

The more I think about this the more I think it is the BIOS turning off the system due to CPU overheat, I had exactly the same problem once.

Look in the BIOS and see if it has a setting that sets the temperature at which it shuts off.

You can force the issue with cpuburn (google it) there are different versions for different CPUs, choose the one for your cpu, It will cause the CPU to heat up rapidly and if it triggers the shutdown then there is a good chance that is the problem.

Check the BIOS to see what temp it is set to shutdown at, and check the CPU specs, it may be set too low, if not you will need a better CPU cooler, or a bigger fan blowing on the CPU cooler.

You might want to consider stress testing your machine with different hardware components attached (ie, take out all unnecessary components and start with individual RAM chips) and reconnecting your wires. If its still failing, then you know whats left (CPU, MOBO, PSU).

Also, take a look at your capacitors, especially the power regulating ones by the CPU.

I vote for CPU overheating. To test this, try opening your internet browser and going to http://www.webkit.org/perf/sunspider/sunspider.html

Hold down the CTRL key and click the "Start SunSpider 0.9.1 now!" link 50 times or so - each time you click, this will open a new tab and start the test in that tab. This is an intense enough test to max out your CPU if you run enough instances.

Note: Use an inefficient but multithreaded browser. Internet Explorer 8 is ideal for this test, Firefox is also good. Don't use Chrome or IE9 because they will finish the test too quickly, not giving your CPU enough time to heat up. Do not use Safari on Windows either as it is single-threaded and won't max out your CPU.

Open Windows Task manager, as well as CoreTemp (install it from here: http://www.alcpu.com/CoreTemp/ ) and run them while you're doing the test.

By the way, on idle your CPU should be anywhere between 20C and 40C depending on what CPU type you have. Notebooks generally run a little hotter on idle but that's not what we're talking about here.

Under load, the MAX a desktop CPU should be getting to should not exceed 75C if you're using stock settings. Again, notebooks run higher.

Also: Can you share the make / model of your CPU and power supply?

If all device temperature is normal, then I think your MOBO sensor/chip was damaged during the previous power surge, but the damage wasn't apparent until now. Likely your onboard sensor is picking up wrong readings randomly and forcing a safety shutdown.