HP (Hewlett-Packard) nx9420 ユーザーズマニュアル

If the computer you are servicing has an unknown password, 
follow these steps to clear the password. These steps also 
clear CMOS:

1. Prepare the computer for disassembly (refer to 

 for more 

information).

2. Remove the real-time clock (RTC) battery (refer to

removing and replacing the RTC battery).

3. Wait approximately 5 minutes.

4. Replace the RTC battery and reassemble the computer.

5. Connect AC power to the computer. Do not reinsert any 

battery packs at this time.

6. Turn on the computer.

All passwords and all CMOS settings have been cleared.