Flat battery, blown fuse, wire's come off etc.  Did you leave lights on?

On older RHD cars the manual lock is still on the LEFT front door, whereas
on later cars it is the driver's door.

A flat battery can be charged through the boot lamp providing that you get
the polarity right and only trickle charge so as not to blow the battery
supply fuse.  Again in later 7 series the battery is in the boot.

in article
e7f7f257-b18b-4000-b902-cf14450c1e56@j38g2000yqa.googlegroups.com, Chris
Gloss at chrisgloss@gmail.com wrote on 1/18/09 12:17 PM:

yeah ... try powering up the battery or checking connectors as the first go
at it ... usually things don't get pluged in and that is the solution about
90% of the time.  Then there is fuse, continunity and having someone trace
it down and see what broke.  But usually it is just having enough power like
it is suppose to have ... always well sorted out ... works just fine then.

sumbuddie hopes this helps

I have the exact same car here in Florida. In my case I happened used it in
4 weeks. It went completely dead. The door locks wouldn't work. I couldn't
unlock it no matter what. I checked the manual and it said to turn the key
in the left front (driver's door in my car) lock hard to the left as you
lift the door handle hard (but don't break it). The driver side was a little
stuck but the right passenger door opened okay after 2 minutes. I started to
"hard lock" the car after using the key fob to lock it and returning to find
it unlocked due to others having the same frequency in their car locks. My
battery is under the rear seat and the positive lead post is under the front
hood which of course cannot be accessed unless you pull the release inside
the car.

I hope this works for you. It's in the manual if you have one.