The MobilePro 800 has both a Reset switch and a No-serously-now-RESET-damnit 
switch.  The latter is located on the left hand side of the battery tray 
inside a hole.  Remove the battery and power.  You can press the secret 
switch with the stylus, and it should feel tactile but low-travel like the 
power button.

After pressing the no-seriously-now-reset-damnit switch, you should be able 
to turn the unit back on by pressing the Power button, without pressing the 
regular Reset button as is usually required after 'halt -p'.