Dell Alienware M17x R3 (Early 2011) - Manual (Page 99)

System Board 99
26 Turn on the computer.
NOTE: After you have replaced the system board, enter the computer Service
Tag into the BIOS of the replacement system board.
27 Enter the service tag (see "Entering the Service Tag in the BIOS" on
page 99).
Entering the Service Tag in the BIOS
1 Ensure that the AC adapter is plugged in and that the main battery is
installed properly.
2 Turn on the computer.
3 Press <F2> during POST to enter the system setup program.
4 Navigate to the security tab and enter the service tag in the Set Service Tag
field.