I have a Dell Dimension 4550 desktop that died Friday. The computer shutdown fine but when I proceeded to move it from one office to another, it would no longer power on. I spent more hours than I should have trying to diagnose and narrow down the problem and I think I have a good idea where it is.
Stage 1: Power Supply
To test this as the possible cause, I have a ATX power supply tester. It tests the large connection to the motherboard to verify that the power supply is working. I've used this on a power supply that is hosed so I know when it needs to be replaced. When hooking this up to the current power supply, the fan cuts on and because I left the hard drives connected they also spin up. This is completely opposite from what would happen if the power supply were hosed.
Mitigating circumsatances: I don't know if the tester has a way of testing the 4 prong “power on“ connector that connects to the motherboard. It could be that the power supply works but this power on connector does not.
Stage 2: Motherboard
The motherboard has a “standby power“ light that comes on when the power supply is plugged into the motherboard. The network connection has a LED for when the ethernet cable is plugged in and this light also comes on. This light isn't dependent on power and functions even if the computer is turned off. Realistically the computer draws a small amount of power whenever it's connected regardless of the power switch being turned on. Everything indicates this is happening as it should but it could be a false positive. Motherboards can be finicky.
Stage 3: Power switch
This seems to be the only logical choice. This is connected to a board that is mounted against the front of the case and then a proprietary looking cable connects this to the motherboard. From this “I/O Front Panel” another cable goes through the case and connects to the power switch on the front of the computer. I cannot verify this is connected properly because I can't seem to get to the connection. I've tried pulling on the cable slightly and everything seems in place but it's possible one pin isn't seated or the entire thing isn't connected as it should be. It's possible this is not a connection->connection cable but has one end that connects and the other end is fused into the power switch somehow.
Summary
Everything indicates this is a power problem since the computer will not POST. I want to narrow this down to the power supply, motherboard, or power switch before I call Dell and speak to someone I can barely understand. This will also help me bypass their scripts and get right down to the exact issue without spending hours on the phone. If anyone can think of anything I should try, please let me know. I'm fishing for ideas because I'm all out of them and I want to exhaust every avenue before I go the warranty/replacement route.