Hey there, about 2 months my pc started to shutdown by itself, sometimes I turn on it, and after it shutdown, in other hand, when it doesn't shutdown, it works during days.I already changed its power supply, but the problem goes on.I also checked the temperature and it is ok. I really don't know what should I do.

Does the computer turn itself off even before the operating system loads?

And does it just turn itself off as if the power had been cut, or does the operating system go through the shutdown sequence as if you had told it to shut down?

Yes, in general it starts the system and turn off, after it, when I try turn on, it turns off almost immediately, right now I turn on it, and it turn off before the screen to select the system. and it turn off itself as if the power had been cut.

This is obviously a hardware problem, and since you've already replaced the PSU, it's most likely a problem with the motherboard.

You should take a close look at the capacitors on the motherboard for any signs of bulging or leakage, like in this picture. If you see anything like that, replace the motherboard as soon as possible to prevent damage to the CPU and/or power supply.

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Ok I'll check it when I arrive at home, and post back here. Tank you, you really helped me a lot. I also will put here a picture of my motherboard right? tanks!

Make sure to also run memtest86+ just in case. It is likely to be the PSU or mobo tho.

I took a look on the motherboard and I didn't see any sings on the capacitors, but to make sure about that, I took a picture of all capacitors to you see. H_TeXMeX_H I already changed my PSU, about 2 weeks ago, and I'll run the memory test but probaly it is not memory problem. Tank you for help me guys.

Here is the pictures

http://imm.io/1cgK7

http://imm.io/1cgM8

http://imm.io/1cgNF

Some shutdown's can report to some place. Either in bios or in /var logs. Also finding out if the system did a proper shutdown versus a crash help too.

The PSU wasn't a bad choice.

I'd boot to bios and see how long it stays up.

As above, memtest for a few days would be great.

Booting to a live cd/usb would help too if different distro. Even booting to a Barts PE may help decide what is going on.

You're right, everything looks fine.

The capacitors most likely to cause problems like this are those providing the CPU with power. They are located between the CPU and the I/O ports at the rear of the system, and sometimes to the right of the CPU, at the edge of the board. They all seem perfectly OK in your pictures.

As H_TeXMeX_H mentioned, a bad RAM chip can also cause problems like this. Run Memtest86+; it should be able to tell you pretty quickly if your RAM is OK or not. You can download an ISO file from that site and burn a bootable CD.

If you can't get the computer to stay on for long enough to run Memtest86+, and if you have more than one DIMM module installed, you could try removing one and see if that makes the system more stable.

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Make sure the fans are working and the vents are free of dust.

The most common cause of unexpected shutdowns is overheating, although, as you describe the problem, I do agree that it's likely something deeper.

Ser Olmy, I got do the pc to stay connected, I'll do not disconnect it, because if I'll do it, it will turn off by itself again, I can do the test now. I'll download an iso to do this test, tanks for you reply guys! I have only one RAM memory. Frankbell, I cleaned the fans, a few days ago tanks for help I'll check it again.

You could also try looking the log files, but I wouldn't be optimistic. If it's shutting itself down unexpectedly, it's likely not getting a chance to log the reason.

I'd start with /var/log/messages.

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Guys, should I shut down my pc completelly to do the memtest? Because if I'll do it, probally it will start to shut itself down again. Frankbell I've checked the "/var/log/" and I found some logs but nothing about shutdowns, as you said it's unlikely to log the reason. Tanks again.

If you don't want to reboot to run memtest86+, you can use memtester instead:
http://pyropus.ca/software/memtester/

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I can reboot it, I just can't shut it down and after turn on. But I can reboot and run the memtest86+, I already burned it on the disk. I'll do it when I come back from university.