Hi to all, after many years with dell machines I have a problem with an optiplex 390. When I unplug the power cord and eg 1 hour later I put it back on, the machine does not start. I press the button on the psu (back) and the power button turns yellow but the machine does not display anything. The only thing I could find for it to work is every time I take the battery out of the CMOS I put it in the socket and then it starts normally until the next time it comes out of the power. I have already change battery and i load defaults on bios.