try taking the battery out first, then putting the battery back in. make sure that the phone is NOT connected via usb cable, or else it will automatically turn back on.
then use the power and lower volume key to enter bootloader mode.
Current devices: Galaxy Note 2 Stock,Nexus 4-stock, galaxy tab 2-7, galaxy note 10.1
Sensation 4G Bruce cm10 jellybean, Asus TF300, Blackberry Playbook, Nexus 1, SE Xperia x1a,HTC Kaiser,Nokia N80,Sony Ericsson W800, Nokia 9500, Motorolla MPX 300 (winmo3), and dozens more. also have an iphone 3g and ipad2 in the family.