In regular Mode, just after the password is entered, your Mac transitions to using accelerated, interrupt-driven operation. A failure in the graphics system at that point would leave the screen blank.
Contrast that with what should happen in Safe Mode, where the graphics acceleration Driver is never loaded. There, after you enter your password, the screen should stay lit, but screen updates (without acceleration) will be wonky and slow, but ultimately correct.
If this follows my prediction, you may have faulty graphics card.
Safe Mode takes defaults for as many things as it can, and may use a lower screen resolution. Any changes you make and save in Safe Mode (such as changing screen resolution) are intended to "stick" in regular mode.