I know this post is old, but I have a problem with one of my dell computers simular to this and was wondering if any of you believe it is the powersupply as well or something else.
The problem is a little harder to identify as everything works fine when the computer is running.... well that is until you power down and leave the power off for a LONG time.
It doesn't matter how you turn off the computer or if you leave it plugged in (or not plugged in), you simply have to leave the computer off for a half a day or so.
Once you do that, the computer will not post until you first try and turn it on, then unplug the computer (plug it back in) and try and turn it on again. That is the only way it will turn on normally.
If you simply press the power button after the computer is off for a long time, the computer will come on (that is the power light and the fans all come on), but it will not post. Simply unplugging the computer at this point and then plugging it back in will make it start normally again.
This bug is really odd as leaving the computer on for days, running any diagnostic programs, stressing the computer out or even shutting it off and then back on... everything will work fine. It simply only becomes a issue if the computer is left off for awhile.
Any help would be appriciated, thx.
PS. At first I thought maybe it was a bios/cmos battery drain issue or something, but the CMOS battery seems fine when I take it out and run it in my tester. So is it a weird PS reset issue or something? Thx again.