I bought a second SSD to install Debain as a second OS on my Desktop (Win10 as primary OS). After installing Debian from a USB stick, when I start my PC I get a screen where I can choose what to boot (Debain / Windows / some memory tests). Windows still works fine, but when I choose Debian I see a few lines of text / code for a split second then the screen goes all black and nothing more happens.
The trial mode, where you can start Debian without installing it worked just fine, but when I tried installing Ubuntu before I had similar problems (when choosing the Ubuntu USB stick as boot medium I got a ubuntu loading screen then blackscreen without even getting to install it). After a few tries I managed to take a picture of the text:
Loading, please wait...
[ 0.563840][drm:radeon_pci_probe] ERROR radeon kernel modesetting for R600 or later requires firmware-linux-nonfree
So apparently it is a problem with my GPU (VTX3D AMD HD 7870 Black Edition) According to https://packages.debian.org/jessie/kernel/firmware-linux-nonfree firmware-linux-nonfree is a package that includes firmware for various stuff including GPUs. How can I get this package if I can't boot Debian?
Another less important question: When i'm on the screen where I can select what to boot it automatically boots Debian after 5 seconds if I don't do anything. Can I change the default to Windows / increase the time?