My most frustrating computer finally fixed,...I think

For three years, my dell optiplex GX520 has continually tripped from a green light to an amber light while unexpectantly shutting down.  I have tried every solution that I can think of, until the latest one, which I think may work.  Will keep you posted.  I don't want to jinx myself.  I have been through dozens of boards, crying with dozens of other users who have experienced the same issue.  Switched the power supply, memory, hard drive, CMOS battery, data cables, tried every bios setting, updated the bios, tried three different operating systems(XP, Vista and Windows 7), but I think I figured it out, finally, if not by accident.  Ebay, a couple of days and I will let you know if it works...