2010 mac mini - monitor goes dark every few sec's problems since Mavericks Install

Question

My Wife updated her 2010 Mac mini from Mountain Lion to Mavericks and ever since, after start, up the display  intermittently flashes a dark screen, every few seconds.  (within 3-10 seconds or so, there will be another period of dark screen, that may last aprox. 1- 6 seconds.  The timing of this changes constantly.  The finder and all apps I have seen are affected in the same way. it seems to be an all-the-time problem
the monitor is an OptiQuest Q9, and the system connects via an Apple mini display to VGA adapter (supplied with the mac mini) , then a vga cord into the monitor, which has a native resolution of 1280 x 1024.   
The only workaround we have found is to boot the mac with the monitor cable disconnected, then reconnect the monitor cable after boot up is complete. In that case, the monitor does not flash, until the mac is shutdown or restarted again.
Steps I have already tried:
Zapped P-Ram 
Reset SMC (shutdown, waited with power unplugged, then reattached power and  rebootted
Repaired disk permissions,
repaired disk
re-download and reinstalled mavericks fresh.
changed display prefs for resolution, detected displays, etc. 
Changed background picture.
I don't know where to go with this anymore, and it has already taken a lot of time.
Who's got a Fix?    And if there is no fix, how do I revert from Mavericks to Mountain Lion?   The mac mini came with Snow Leopoard.

Answer 1

Problem Fixed!
I found another page that referred to resetting the PMU (http://support.apple.com/kb/ht2183) , which controls things like wake and sleep:
"If the settings in the PMU become corrupted, it can result in operational anomalies such as your computer not turning on, not displaying video, or not waking from sleep, among other things. In these situations, you may need to reset your computer's PMU."
Anyway, it is pracitcally the same proceedure as resetting the SMC (SMC reset=  Shut down, disconnect power cord for 10 seconds, reconnect power cord, wait 5 more seconds, turn computer back on)
but it is slightly different:   (PMU REST = Shut computer down, disconnect power cord for 10+ seconds, reconnect power cord WHILE SIMULTANEOOUSLY PRESSING POWER BUTTON, let off power button for a few seconds, then press power button again to restart the mac mini.)
After this the display problem was fixed, but the fan ran at high speed, so I did one more SMC reset as described above. Now everything is in order.   This also fixed the issue of the mac mini not waking from sleep unless the power/sleep button on the mini was pressed (it wasn't responding to the keyboard to awaken). Now it's all good.
Hope this helps somebody else...