Today I went to use my iMac purchased in 2008. I tried to power it on and it wouldn't turn on. I checked the power cord. Everything is fine with the outlet. I unplugged the power cord, unplugged the Ethernet, and tried to turn it on again. This time it started. I was flooded with relief. But after about two minutes it randomly shut down again and won't turn on. What could be causing this problem? It's been working fine until now and it definitely is not overheating... Could it be a power surge or something wrong with the socket or is my computer just dying?