I have a dell xps 200 that will not power on. I have no lights on ,other than the green led on the motherboard. I have tried testing the PS and it checks out good. I have done the regular process of elimination on the cards and the hdd,cdrom ETC.... The processor has been changed with a known good one, and the ram has been replaced with good sticks. I have tried to clear the cmos, and take the battery out for a while, I also tried to discharge any static electricity by holding the power button down for about 60 seconds. I am at a loss as to what to do, please any suggestions would be appreciated.
Time for a new board and possibly ram. I would check ebay or craigslist for used boards. Your dell case may take a standard micro atx board; you should inspect the backplate and see if it's removable. You will have to reinstall windows with some motherboard changes. If your windows copy is dell proprietary, then it may not be re-activated by microsoft. You'll just have to try it.
I have an XPS 720 with a similar problem. Unplugging the power for a LONG time allows it to power on (12-24 hours or more). Today even that did not help (24 hours plus). The amber main-board light comes on when the power cord is plugged in, but the fans do not spin as normal startup, and no other lights come on.
I unplugged the MAIN POWER plug from the Power supply to the main-board, and this "fixed" the problem today.
Unplugging the power cord, the amber main-board light will fade away after 20-30 seconds, but still no power when plugging it back in. I believe there is a SMD capacitor that is not discharging when power is removed, keeping the power from starting.