i charged my battery and now i dont get any power why?

Have you tested your battery to make sure it is holding the charge? Sometimes batteries get dead spots in them that wont allow them to hold a charge. When you say you dont get any power, do you mean that nothing works that requires power, i.e. lights, gauges, radio, windows( if you have power windows), or that the car wont start?

Exactly. A battery is made up of connected cells. If one of those cells goes bad, the battery can be jumped and perform fine. However, the alternator will not be able to generate enough of a charge even after running a while. If you shut the vehicle off, the battery will be more or less dead. This sucks. I know. My factory battery in my E39 finally died after 12 years!

I agree with the other two that it might be a battery issue. To test this put a charger on the vehicle and see if everything works normally then is most likely a battery issue. If not then you need to start checking fuse, bst (battery saftey terminal). Hope this helps.

I replaced my battery with new one in my 2006 bmw 750i but dashboard shows low battery.

I replaced my battery with new one in my 2006 bmw 750i but dashboard shows low battery. -- --> Did you registered the Battery in settings ?