Download and install Visual BCD Editor in Windows 8 (http://www.boyans.net).
Start tool, right click in left pane and select "Create missing Windows loaders".
It is strange that Windows 8 installation did not pick up Win 7.
Pay attention that mixing MBR- and GRP disks can lead to problems.
To check format of disks and partitions the best tool is still diskpart.exe.
>list disk - tells you if disk is MBR or GPT.