Well first, I would not let your "friend" touch the PC again.
The problem is that Windows does not recognise your new graphics card, it is looking for the old one.
I think what you need to do is boot the PC with basic graphics, THEN install the drivers for the new graphics card, then reboot the PC.
As the computer is starting up press the F8 key on the keyboard. This will take Windows into "safe" mode.
Choose one of the options which says something like basic settings or default settings.
This will start Windows with a basic graphics driver.
You should then be able to install any drivers and programs that came with the graphics card, or maybe let Windows install the drivers.