There are several reset methods for the WDT90 & WDT92 mobile computers/devices.

Warm boot terminates an unresponsive application and clears the working RAM, but preserves the file system. The Registry is restored from persistent memory if available or returned to factory default.

Cold boot forces all applications to close, completely reinitializing the system. It clears the working RAM, but the file system is preserved. The Registry is restored from persistent memory.

Clean boot restores the device to a clean configuration: both the Registry and the file system returns to a clean status that conforms to factory default.

Warm Boot

To perform a warm boot, press and hold the following keys simultaneously: Amber + Blue + ESC

Cold Boot

To perform a cold boot, do the following steps:
1. Turn off the device by pressing the ON/OFF Power button.
2. Squeeze the battery latch and remove the battery pack.
3. Simultaneously press the SCAN key and the Reset button in the battery compartment for about a second, then release. The Reset button is beneath a rubber circle; you should feel a click when the button is pressed properly.
4. Insert the battery pack.
5. Turn on the device by pressing the ON/OFF Power button, then release. 

Clean Boot

To perform a clean boot, do the following steps:
1. Perform a Cold Boot following the instructions above.
2. Promptly after resetting, press and hold down the 'Esc' + '0' keys simultaneously for a few seconds until a dialog box appears asking for confirmation. When the message appears, release the keys.
3. Press the Enter Key to complete the Clean Boot.

The Cold and Clean Boot procedures requires some manual dexterity and proper timing to complete successfully. Here is a video showing the Cold Boot then continuing to the Clean Boot:
https://dl.waspbarcode.com/kb/mobiledevice/wdt90/WDT90-Clean-Boot.mov