Ubuntu 15.04 flashes log-in screen then black
I too built a desktop, and used the 750Ti. I had the exact problem that the OP has, and I can personally testify that the below worked for me. I don't have a ton of time, so I'll have to summarize. When in doubt, Google is your friend.
Go to NVIDIA's website from another PC and download the appropriate driver to a USB drive.
Plug this USB drive into your desktop and boot. At the login screen, enter runlevel 2 by pressing CTRL+ALT+2
Now you will be in a terminal (fun times!). Login using your account.
Kill lightdm.
Mount your USB drive and un-tar the driver.
Run the driver installer. If there are no errors during installation, then reboot. The login loop should now be gone.
This makes it sound simple, but unfortunately, it is actually pretty difficult. It took me four tries to get it right.
Let me know how this works for you!