Need help with monitor and graphic card

I already posted this at NRaas, but perhaps here are some people who can also help me, if there is a help. :s
More post, more help hopefully...
Yesterday I worked with my computer, put it off and after a while, turned it on again.
Black screen! But it said: no signal, so I guess the screen might be ok?
But there was no way that I got a picture on the screen.
Then I put an old monitor to the computer and everything got crazy. The graphic card is not shown as installed anymore. Instead there is installed an Intel Hd Graphics 4000 graphic card (normally I have an AMD Radeon R7750 core edition card installed).
My ongoing game isn´t playable anymore, it freezes soon after it loaded. I can play a new game....
The Device config looks like:
https://i.imgur.com/hBaa94d.jpg

And I now have my normal monitor connected with the computer again and it works, but not with the horizontal slot. It works with the vertical one.
So is the horizontal slot broken? Do I have to install the driver software again, because it deinstalled? Can I change the horizontal slot somehow? (I don´t even know how it is called)

Any help is needed, I´m completely lost!