First of all unplug any audio accessories, might make a difference might not, I also disabled dolby audio on my ROG ally so maybe that makes a difference, but this definitely made it work.

Right click on rocksmith in your steam library, manage, browse local files, right click rocksmith.ini and open in notepad.

Set exclusive mode to 0 and Fullscreen to 0

It should boot again and work just fine, if not, try this on a different machine.