Computer does not start but fans turn

I want some help on my computer. Indeed, it refuses to boot. Sometimes it goes out, at any time. And when I restart, nothing appears on the screen, and fans (well especially that of the graphic card, the processor I do not know it is not very loud) turn out like that. I first thought about a problem of overheating, however I left it to cool and it does not restart. Also dust, I cleaned the fans. I also tested by removing a strip of ram, then the other.

I explained that in those moments, the only way to shut it down and turn off the power behind, it does not address the power button or reboot. Usually I turn it off, turn once or twice and it went there but refuses ...

I also searched a bit and I looked at the system log or once it had been extinguished, and I saw that there was this time precisely to the times when my computer died.

Is it serious? Is there a solution or do I contact the manufacturer? I am getting the error code 12, source:ACPI.

my config:

Motherboard: Gigabyte GA-MA790X - DS4
AMD Phenom 9850
Ati radeon HD 3870 512 MB sapphire
and 480 watt power supply

My first intent would be your power supply. Your power supply is probably a noname.

Thank you for your reply

My power supply is a cooler master from what I see above. Indeed few months ago, I had problems with: my ram, then the motherboard. I got a lot of errors and I was advised to do a memtest, what I did in finding errors in the ram. So I returned the strips, and gave me new ones. However, the PC did not want to start at all and incessant beeps, and I had it back in full. Apparently it was the motherboard that I have been changed too.

Finally I do not know too, if cooler master power supply is correct or not.

Cooler Master does not manufacture its power supply and apparently often change suppliers, so difficult to know whether that is power supply in particular good or not.

Also the symptoms that you describe still orient towards the power supply.

A good power supply brand (Corsair, Antec) of 350-400W enough for your config. That would be a good investment I think (hope not to get you to the wrong track). There are modular or not, etc .

Could it need a BIOS update?
Check all cable connections, and make sure cards are seated properly. I once had a problem on a Mac that was related to connections.