Which rom do you have installed on your phone?
Stock roms don't have any recovery out the box (both gingerbread and ICS). Plus, on stock ICS, using the key combo will wipe data imediatelly without asking.
First, you need to flash a patched v20 with cwm recovery.
Sent from my LG-P970 using Tapatalk 2
SAMSUNG GALAXY TAB 7.0 PLUS P6200 (STOCK ROOTED JB 4.1.2 ROM) | LG OPTIMUS BLACK P970 (MACKAY ROM 2.12.5 + CWM TOUCH 184.108.40.206)