The screw that you have showing on your picture needs to be removed or you cannot get panel odd.

The plastic piece needs to come off before you can get to screw. By moving the inside door handle you should be able to unhook the rod that connects. After this is done then you can remove panel.

Your pictures look similar to the 190E that I have.

With the door panel removed you should be able to put power to window regulator by using a hot lead to check if it is working. (auto body repair shops checks them this way.)

You should be able to get a replacement part for the one you cracked. MBZ usually keeps these parts in their warehouse.