Are you using the generic broadcom Windows driver, or did you download one from their web site? I had this very same issue on a mobo with a broadcom NIC a couple of years ago. Everything worked fine until I downloaded the Windows driver from their site and installed it, after that it wouldn't work in Linux. When Windows shut down the LED's on the back went out and never came back on until I booted to windows. The way I fixed it was to download the Linux driver from their site and use it instead of the default kernel module. When I did that, everything worked fine.
Not sure if this is the problem in your case, but you never know.