If you are certain it is not an electrical issue, it could be fuel related. The car cranks and won't start sometimes? Have you changed your fuel filter? Your fuel pump could be on its way out. What maintenance have you done to your car so far? Do you have a check engine light? Checked for codes?
P46 Projectors + FX-R Retrofit + 6k D2S / 60 LED AE's / Smoked LED Tails / Smoked Turn and Side Markers / BSW 10" Sub /ZHP Knob / Matte Black Grills / DICE / Parrot + Connects2 / OEM Alternative Alarm Mod / Clutch Switch Delay Mod / M3 Rep Front Bumper / 3M Black CF Di-Noc Wrap / K&N Intake / 35% Tint All Around / Black Short Eurotray / 545i Shifter