I *think* I have a unique problem, have scanned through these pages and not found anyone else post anything similar...
I have a launch Black Lumia 800 (November 2011) so I assume it has the unlocked bootloader however there doesn't seem to be a way to check.
I've tried the following
Hold VOLUP + VOLDOWN and connect the USB cable at the same time, screen goes black and Windows indicates a device plugged in with the standard sound... Nothing shows up in Device Manager however. After about 10s the device disconnects and the Lumia proceeds to boot as normal.
VOLUP + POWER Device boots as normal
VOLUP + VOLDOWN + POWER Device boots as normal.
Devices: HTC Charmer (Sold), HTC Touch Diamond (Broken), HTC G1(Sold), HTC Desire (Sold), HTC HD7 (Broken), Samsung Omnia 7, Nokia Lumia 800
OS's Used: Symbain Series 60, WM6.5, iOS, Android 1.1-2.2, Windows Phone 7
Computer Science Student at the University of Birmingham.