I just built a new PC, and when I turn it on, it goes for about 3 seconds and then turns off. I disconnected everything except the RAM, and CPU and still the same issue. For the 3 seconds, everything seems to be working: fans spinning, lights on. Unfortunately, my case does not have a speaker, so I cannot hear error code sounds if the MB is giving them. I'm going to try to find a cheap speaker tomorrow. Anyway, I'm mainly posting this to see if anyone has had a problem like this before? Any ways to narrow down the problem? The specs of the new computer are: Asus M2N-SLI Delux Athlon 64 x2 5600 Kingston HyperX 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel 500 Watt Power Supply

I've had problems like that a few times before when building PC's.

Every time my PC has turned off while trying to boot it's been because the PSU didn't have the wattage required to power the new CPU I had just stuck in.

A 500W sounds like it should be powerful enough for your needs, but I've found that "no name" brand PSU's are often less powerful than they say they are. Perhaps you should try another PSU anyway?

Another thing to try is clearing the CMOS. After I changed the case on my computer it turned off and on when I tried to boot it up, and clearing the CMOS fixed that. Check your motherboard manual on how to do that.

But as Hodgman said it's most probably the PSU.

I remember with my mobo/cpu combo i had i forgot to plug in a cable right next to the CPU and nothing worked. It was a square 4-pin connector.

My bet's on the thermal paste between the processor and it's fan. Remove fan, put paste (more paste).

1.5$ and 5 minutes for the full experiment.