If you can boot up into the Advanced Boot options by tapping F8 as you switch on, although this key combo can differ with makes of computer - select Repair your Computer then navigate to the Recovery Environment (RE), you can try Startup Repair and run that up to 3 times if at first unsuccessful.
If that doesn't do it you will need to fix the Master Boot Record (MBR)
This is done with the Bootrec commands and is normally done after booting up with an install disk, but as your version is probably now SP1, the install needs to include SP1.
These are the Bootrec cmds you can use -
https://support.microsoft.com/en-gb/kb/927392However, if you don't have an install disk and you can boot up into the RE and select Command Prompt, the cmd
bootrec /fixmbr or the others may work.
There is a space before the forward slash.
Enter
exit to close the cmd window then Restart.
If it's still a no go up to now and you have access to another machine (don't know what you are using to post with), you can create a Paragon Rescue disk which can repair the boot sector for you.
https://www.paragon-software.com/home/rk-free/Click on the Download & User Manual link.
