I can't write if there's music with words in it being played.
My mind takes the words coming in my ears, and completely blocks the words coming out of my fingers.
However, when I'm writing and I hit a point where the words are jumbling together trying to come out, I find that if I step away from the screen, and listen to some music away from my writing area, it sometimes resets things, and the words start coming out in order again.
When I was writing 'Blood On The Sand', my initial story was supposed to end in the souk, eating tajine with Bob Reno, but the words started piling up, so I went into the backyard to pace with my Pandora app on my phone.
This song came up, and I listened to it three or four times before coming back inside and writing the final scene.
Rather proud of the last bit. Some folks have offered that it's a bit cheesy, but I'm a sucker for the old pulps, where the good guys are good; the bad guys lose; and there's at least a chance of happiness no matter how crappy things are.