HP Pro 3400 Maintenance And Service Manual page 165

Computer seems to be locked up.
Cause
Program in use has stopped responding to commands.
Solution
1. Use the task manager to close programs that do not
respond.
2. Attempt the normal Windows "Shut Down" procedure. If
this fails, press the power button for four or more
seconds to turn off the power. To restart the computer,
press the power button again.
Solving Hard Drive Problems 155