Automatically Turn on a Computer at a Specified Time

Move down to Step 1 to find an easy way to get your PC to power up automatically.

Steps

Restart your computer
Press delete when you get to the screen that says "Press DEL, F1 or F2 key to enter SETUP or BIOS."
Use the arrow keys to find the "Power Management" tab. Scroll to "Power Up Control. " Press enter.
Scroll to "Resume by alarm / Power up by alarm. Enable it.
Select wake up Day/Hour/Minute options. (select Daily in wake up Day option, if you want PC to start daily automatically at given time).
Press "Esc" on your keyboard when you have reached the desired power-up time. Say yes when it asks for confirmation of the changes.
Wait for your computer to reboot. Turn it off each night. It will boot itself up at the desired time.

On a Macintosh you can bypass all the complicated rewiring and reprogram your computer.

Go to System Preferences.
Click on the "Energy Saver."
Click on the "Schedule" button.
Check the box that says "Start up or Wake." Select the frequency you would like it to do so from the drop down menu, and use the arrow buttons to choose a time. Repeat for "Sleep" if desired. Press "OK" when done.

Make sure that the timer is set to a time when you would not be working, as otherwise you may lose work when the computers power fails.
Make sure any cable is unplugged before you do this. There is quite a lot of electricity going through a computer, even if the power on the computer is off.
Taking apart your computer will void the warranty, and you will not be entitled to any free service. Also, doing this will immediately remove any sale value in the future (people normally want a normal computer, not one with a mind of its own).
It is very important that you wear a grounding bracelet while doing this. you can completely fry your computer if not careful.