HP Compaq Presario,Presario 800AP Supplementary Manual page 112

Q. My display (monitor) is blank. What should I do?
A. Your Notebook might be in either Sleep (Standby) or
Hibernation mode. Try pressing any key to wake your Notebook
from Sleep (Standby) mode. If this does not correct the problem,
press the Power button once to resume from
Hibernation mode.
Q. There is no sound coming from my Notebook. What's wrong?
A. You can control the sound coming from your Notebook
speakers by double-clicking the Volume icon in the taskbar.
The Master Volume window is displayed:
Make sure the Mute all box is not checked in the Master
Volume Balance section.