[SATLUG] Troubleshooting Time

[Arthur Hall]

A donated PC has the lights come on and the fans spin, but it doesn't POST.  The power supply tester shows all voltages glowing green.  All the connections are solidly seated.  Tried replacing the RAM to no avail.  CMOS battery is good.  Haven't tried replacing the IDE ribbon yet, but I didn't think that would inhibit the POST process.  Any ideas?
Thanks in advance.
Art