I have bought HDMI to Mini Displayport and HDMI cable from MonoPrice. When I boot MacBook Pro, I got 2-3 seconds gray screen and 2-3 seconds Background Default image. Then nothing, NO SIGNAL, says my TV Edit: I tried with Guest Account, works perfect, when I login my account, no signal
Sounds like you just have the external display set to a bad resolution. Go to the Displays panel in System Preferences, click "gather windows," and then change the resolution to something else.