I have Mac mini 2011 and Samsung Syncmaster 710v (old TFT monitor) connected through mini DisplayPort to VGA. The monitor shows something only when the login screen appears (no boot menu, no boot-loading, just black screen, BUT no info that the monitor isn't connected).
On new monitors (VGA), my Mac works great and I can see the boot menu. Is it the monitor's problem, a mini DisplayPort issue, or software?