Hard Reset your Windows Phone 7 device (WP7)
Had some issues when removing a 32Gb micro SD card from my Samsung Focus WP7 phone, it came back saying that the SD card had been removed and to either put it back in or reset your phone, it then went on to say read your manual to figure out how to do the hard reset (didn't find anything in the manual!). If the phone is running then the hard reset is rather easy (Settings -> About) but when the phone is not working it's a bit more of a challenge… This is how I did it!
1. Press and hold the Camera, Volume Down, and Power buttons simultaneously.
2. Release Power when the phone vibrates, but continue to hold down Camera and Volume Down.
3. Release Camera and Volume Down when the Format prompt is displayed on screen.
4. Press 
.
5. Press 
again to confirm the hard reset.
Copied this from:
http://www.technipages.com/samsung-focus-hard-reset-using-hardware-keys.html