Optiplex 755 MT singular video during POST (with solution)

PC posted normally with Dell logo in the pm.  C2D DDR2 ram dual channel.

At night after a psu swap, power on, no Dell logo on screen but a full screen of regular array of ”””””””””” displayed with a blinking cursor (looks like _) at top left corner of screen.  On background there is faint flickering light dancing like a ghost.

at one time, the whole screen ”””””””””” becomes all tiny diamonds.  

No beep.

never seen this before. prior experience with post is either normal logo or no video.

motherboard video adapter broken?  Monitor is verified good using another Dell.

Trying reset CMOs jumper, or remove CMOs battery, no change.

Finally, after removing all ram and put only one back, get back normal post Dell logo.

add second ram, still good, add rest of ram, strange video reoccurs.

Solution: replace those “bad” ram.

It is possible that those “bad” ram cause POST to stall (yet no Dell logo at all), thus the blinking _.  But that does not explain the singular video.