HAVE you tried to remove the battery and than PLUG the AC in ? SEE if this helps and if that doesn't put the battery back in and take the AC out and TRY it again.
IF that doesn't WORK you may have your computer set on Hibernate or Sleep mode? THIS is in your control panel in the start menu under the POWER SETTINGS...... You should see the problem if you do get the computer running again and it happens again.

Also try to hold down the power button for 5 seconds or until it beeps and than push it again to reboot...

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