This is a long shot, but could you check to see if there is a disk in the CD/DVD drive?
Here is some tutorials to clarify and help you do what Kaktussoft is suggesting:
To get to the advanced boot option screen: Advanced Boot Options
And then select "Repair Your Computer"
To get to a command prompt once inside : System Recovery Options
And then choose "Command Prompt"
Then you can follow Kaktussoft's directions.
Hope that helps