Help! Rescue mode

I recently tried to install Debian (Linux) with a friend of mine on my computer.
The installation guide was completed correctly but I couldn't start the Debian OS (nor the repair mode)

However, I could still start windows vista...

I tried to install it again without using the VNC while installing it on the disk but after the whole installation, the pc loaded rescuemode after starting up again.

What should I do now?
(I installed it on an external drive, however the error comes back after installation)