hi hope this helps
1. Shutdown your PC.
2. Turn on your computer and enter boot setup, The key for this is different for every PC and is usually displayed in the top right hand corner, on my PC the key was F2.
3.Skip through the pages of your BIOS by pressing " ALT+P " this may differ from system.
4. Come to a page called " Power Management " if you do not have a page called this, Look on each page for two things saying " Auto on mode " and " auto on time ".
5. Turn " Auto On Mode " to Everyday Or weekdays, Then Turn " Auto On Time " to the time you would like ( It's in 24 Hours Time ).
6. Press ESC or the exit key you have, And if it prompts you to save your changes, Hit save.
7. Restart your computer and it will now automatically boot if your PC is off at that exact time.
(on laptops i think you have to have the lid open and the power off)