This could be a couple of things.
It could be a wiring problem that is isolated to the front windows only (would require further diagnosis by a competent automotive electrician), or it could be an issue with your general module (the module that controls most of the cars body functions).
There are several relays inside the general module that go bad and cause the windows or central locking to stop working.
The cheapest way to test if this is indeed your problem is to swap in a unit from a similar car. If you don't have access to a similar car, a dealer should be able to confirm the problem by hooking the car up to a BMW tester and interrogating the module.
If you would like to work on this yourself (ie swap in a new unit), you can locate the general module behind the glove box in your car. It is a white rectangle as in the picture below.
I hope that helps. If you are satisfied with my help, please click the green ACCEPT button below so that I am paid for my time and effort. I will continue to answer follow up questions should any arise. I do not receive anything until you press ACCEPT.
Thanks and good luck with the 323,