I am trying to setup PHP5.6 on Windows 2012 Server using FastCgi configuration but site returns this error " The FastCGI process exited unexpectedly ". Any idea how I can setup php5.6 with HC Panel using fastcgi mode?

If you're running PHP 5.5.x on your Windows box then you need to ensure that VC++11 runtime is properly installed which can be downloaded and installed from the following:
http://www.microsoft.com/.../details.aspx?id=30679

Make sure you download and install the x86 version (vcredist_x86.exe), PHP on your Windows 2012 box which shall fix the problem.