It took me a while to get the volume down and power to work for a screenshot. I found that I was just clicking the two and nothing would happen. You have to hold them both down for about 2 seconds and it should screenshot.
Not sure if this will help, but it could in the future. There's this app called PushBullet that connects your phone to your computer. All of your contacts with their numbers would be there. If you have it, then you could use that. If not, I highly recommend it in the future.