press F8 repeatedly at boot and choose "Repair your computer"
Click on the Startup Repair link from list of recovery tools in System Recovery Options.
or
press F8 instead repeatedly at boot and choose "Repair your computer"
then Select Command Prompt and type the following commands (pressing Enter after each one):
bootrec /fixMBR
bootrec /fixBoot
bootrec /rebuildBCD
Note: there is a space before the /