In Device Manager, select View and enable "Show Hidden Devices" and check under Non-Plug and Play Devices for something about bluetooth?
If it's there, check the name of the bluetooth protocol?
(Mine was called btkrnls.sys and it resides in the c:\windows\system32\drivers directory)
If there's no sign, I suspect it's time to start from scratch and install a new bluetooth stack. You can download Broadcom's version (used to be Widcomm) from
their website.