Normally, after removing power, it may take up to 3 minutes for the door to unlock

Manually Unlocking the Door Lock System:

1. Unplug washer or disconnect power.

2. Remove the lower kick panel.

3. Reach up along the inside of the front and locate the bottom of the door switch/lock unit.

4. Located on the bottom of the door switch/lock unit is a tear-drop shaped tab.

5. Gently pull the tab down about a ¼" or until a click is heard.

6. The door may be opened.

Source: Whirlpool Duet HT Front Loading Washer GHW9400PL Locked Up!