HP DC7800 doesn't wake up
Configure your Windows 7 PC to go into sleep mode automatically when it is not used for a certain amount of time. Click "Start" and select "Control Panel." Click "System and Security." Click "Power Options." A menu opens. Click on "Choose when the computer sleeps" and select the number of minutes of inactivity. You can also set a separate time interval to put your monitor into sleep mode. If you set both to 10 minutes, then your PC and monitor will automatically go into sleep mode after 10 minutes of inactivity The computer will power-down and turn off unnecessary systems, including the monitor, while keeping the memory active so it can start back up quickly and still have all programs up that were being used prior to entering sleep mode. While this is a helpful feature that can extend the battery life of a laptop, it can result in errors where the computer won't power back up. You can usually solve the problem quickly.
Look for a sleep-specific key on the keyboard. It will usually be near the top row and have a symbol of a moon on it. Press this key as some laptops only respond to that command to come out of sleep mode. Press the "Enter" key to see if that will cause the computer to respond. Move the mouse back and forth several times and click the mouse button. Hold down the power button for 5 seconds if the previous methods have not worked. This is another common method for exiting sleep mode for many laptops. It may also trigger a full computer restart which would also solve the sleep mode problem. Unplug the laptop and remove its battery.
Reinsert the battery and then plug the laptop back in.
This should cause a full restart when the power button is pressed. Download the latest video drivers from the website for your video card manufacturer. Old drivers can sometimes cause problems with the laptop's power functions. See if your computer manufacturer has an updated BIOS on its website. The BIOS (basic input/output system) is the firmware that controls the initial boot processes for your laptop. Computer companies will release updated BIOS firmware if they get multiple complaints of boot or power problems. The BIOS interfering with Windows Power Manager is a frequent cause of sleep mode problems. Adjust your BIOS settings by rebooting the computer and pressing the appropriate function key when prompted on start up. It will normally be F1, F2 or F3, and you will often see a message during start up saying to press that key to enter the BIOS. Experiment with the BIOS settings by scrolling through the menu and locating Power Management. Increase the amount of time the BIOS allows before hibernating to make sure it is higher than the the Windows power setting. This can help eliminate conflicts between the BIOS and Windows concerning power shutdowns.