Cannot install Ubuntu 15.10

I'm new to Ubuntu and managed to install version 14 some days ago. That was already really problematic, but somehow worked. I have a GTX970 graphics card, which is not supported by the nouveau driver (AFAIK).

Today I've tried to update to 15.10 and it failed miserably - so my installation is now broken - which is not a big deal - I just want to replace it with a fresh install of 15.10 from a USB stick (created with Univeral USB installer).

Booting from the USB basically works, but the desktop is not useable - the mouse pointer is invisible and many errors show up, so I cannot do the installation.

I've found quite some help on this, but nothing seems to work. i.e. this answer https://askubuntu.com/a/709131/523935 tells me to try to add nouveau.modeset=0 to the linux command in grub2 - but when I do this, the desktop does not even start up - I end up in a terminal, which asks me to login (to the LiveCD environment). But I don't know which user/password to use (I've tried: "ubuntu"/blank, "ubuntu"/"ubuntu", "linux"/blank, "linux"/"linux", ..)

any ideas?

To install Ubuntu on a system with a discrete graphics adapter that is entirely unsupported an option would be to

• physically remove the graphics card to boot with the inbuilt graphics adapter, or if supported disable the graphics card from the BIOS.
• install Ubuntu using the inbuilt graphics from APU or motherboard
• install the proprietary graphics drivers needed to support your discrete card, e.g. by enabling ppa:graphics-drivers/ppa
• perform a full upgrade of the distribution
• re-attach the graphics card physically or in BIOS

For Nvidia also see

• How do I install the Nvidia drivers?

For AMD/ATI see

• What is the correct way to install proprietary ATI Catalyst Video Drivers (fglrx) directly from AMD?