My computer sometimes (maybe once every 3 or 4 days) completely locks up and there's this loud buzzing noise coming through the speakers. The only thing to do is a hard reboot. This happens mostly when i'm on the internet, sometimes with iTunes running. It happened I think once of twice while I was playing a game. Every piece of hardware in my PC was bought this summer except my power supply, my graphics card and my hard drive. At first I thought my hard drive was the culprit, so I ordered a new one. The problem hasn't changed. I know it's not that problematic seeing as it doesn't happen alot. I don't think this is due to overheating, there's no dust in the case and temperatures at boot are fine.
From the research I've done in Google, some people suggest it's a memory problem, some suggest it's power supply related. Since my power supply is the oldest piece still in my computer (it was installed more than 3 years ago) it might be it.
Specs: Core i7 2600-k, 8Gb DDR3, GTX 260, ASUS P8P67-M, 750GB Sata3 HDD, and I don't even remember how much Watts my PSU has...
1) What could be the cause?
2) If it's RAM, how to test it?
3) If it's PSU, how to test it?
PS: Sometimes I get another problem, my computer will go on the some kind of unscheduled sleep but my mouse and keyboard are offline (lights on them are off) and there's no way to get it back to work. So I hard reboot. This also happens once in a while, maybe 2-3 days. My friend on Steam tells me my status is set to away during this "sleep", so my computer is not locked-up.