Due to the way your BMW's electrical system is constructed, the headlights may flash or flicker as the car is being started if a component of the system is failing or on its way out. The most common and likely culprit of this problem is your BMW's battery. If this symptom has just started to happen, it may be prudent to check the age of your current battery, as it could be aging and losing its ability to hold a charge. If this symptom is constant for you and prevents you from driving the car, you will likely need to replace your battery.
Check the connections of the positive and negative terminals of your BMW's battery by going to the battery directly. If the connections are loose, then tighten them with your fingers or use a rubber-handled adjustable wrench.
Check the charging ability of your BMW's battery by turning the car off, but leaving all of its interior electronics activated. Be sure to have jumper cables and another car with a good battery nearby that you can use to jump-start your car if, or when, it dies. If your BMW's battery and electronics die out in a short period of time, you can likely determine that the battery is losing its ability to charge.
Check if your BMW requires a jump-start on a regular basis to get going. If this is the case, then the battery is likely completely dead and needs to be replaced.
