I have no idea what distribution you are running and I do not use GRUB myself, so I cannot give further help.
You need to get the system in runlevel 3, and it should come up in textmode.
This is normally done from the bootprompt but apparently not with your system.
What you have done (installing on a different monitor) is not good. It would kill Windows as well.
This week I installed a Windows system with a PS/2 keyboard and it had to be used with a USB keyboard. It did not work because Windows detects new hardware after you log in, and you cannot log in because the keyboard does not work.
The same thing would happen with the monitor, I presume.
You are only lucky that the resolution Windows chose on the store monitor also worked on your monitor.
Next time, install on the monitor you are going to actually use. That will solve this problem for sure.