Just acqured a used Alienware Desktop Computer and it won't power up

[Phil]

You either have a dead power supply, perhaps the one you tried was not compatible, or the motherboard has a problem. The fact you aren't even getting the POST screen rules out memory, disk drive, etc. I've had an alienware laptop for 15 years and it still works. Huge, heavy with metal cabinet, extra cooling and so forth as has been mentioned. I would imagine the desktop versions are similar.
Bad video card would keep you from seeing the POST screen but you would still be seeing fans, lights come on and so forth.

[Electronic M]

Originally Posted by Phil

You either have a dead power supply, perhaps the one you tried was not compatible, or the motherboard has a problem. The fact you aren't even getting the POST screen rules out memory, disk drive, etc. I've had an alienware laptop for 15 years and it still works. Huge, heavy with metal cabinet, extra cooling and so forth as has been mentioned. I would imagine the desktop versions are similar.
Bad video card would keep you from seeing the POST screen but you would still be seeing fans, lights come on and so forth.

Most likely as you said. I mentioned making sure things are connected right as I have had a couple of cases of motherboards playing dead when ram was installed in a rush and cockeyed enough to short socket pins.... I've also on a different occasion had ram modules short internally and cause playing dead. Making sure hardware works out on other gear or is new is important.

May also want to sub the CPU clock battery... Earlier this week my laptop played dead on me because the little 3V clock battery which has been dead for months somehow got worse. I think I have seen similar at some point in the past too.