I am having a very similar problem. Was travelling this weekend and I came out to start the X5 on the first cold morning it has seen this year and it cranked, but would not start. My first guess was the fuel pump because I couldn't hear it prime. I checked voltage at the fuse #47 on my vehicle and it showed sub 11V, not sure if this is normal or not. It showed the same sub 11V at the fuel pump. I ended up hot wiring it from the jumper posts in the engine compartment which showed 12V. I let it run and switched on the ignition and it started right up. Did you try hot wiring the pump? How many volts are you getting at the fuse and at the pump?