Over the past few days I have had three Dells (1 Precision M6400, 2 Optiplex 740) where their Broadcom 57xx NIC driver has just died. The driver, not the card. By removing it from the device manager and restarting, following through the new hardware wizard to reinstall the NIC, it is repaired and ready for use.
Just a little suspicious that three machines in two days have had this issue.
Makes you think. I will post any more info if I come across it.