I think I know what the problem is.
You gave just the right clue - unplugging PC!
Your Bios has reset to default
s & a time and day previous to your Windows 7 install (prob date = 2004).
Coz of the hidden M/soft spystuff? built into Win 7, it will refuse to start up!
The answer should be to set the time and correct day/date in your bios.
Then you will have Windows 7 back working again!
tell us how you get on!