I'm sorry, I'm not very good with computers, but I'll try my best. My Dell Optiplex SX270 won't turn on after I accidently unplugged it. When I contacted Dell they told me it was either the RAM, the motherboard, or the CPU. Before I go out and spend a bunch of money on any of these parts, I want to know what the problem is for sure. Thanks in advance. EDIT 1: I'm pretty sure it's not the PSU because I tried out three different types on it and none of them worked (I actually have two SX270's, and a spare power supply).

Don't start replacing parts without troubleshooting. What happens when you try to power up? No fans, no LED's, no POST beep...nothing?

Absolutely nothing, but the motherboard light is on.

It will probably end up being the motherboard, but that's no guarantee. If it was the ram--and everything else was OK--you'd be getting a ram beep error and you've pretty much eliminated the power supply as the problem. But try this: disconnect all the drives and remove all the cards except video. Then see if you at least get a posting screen. If so then the problem is with one of the removed items.