I had the very same problem and tried many of the solutions given here, but to no avail. So I went and bought a new controller and paired it to my Xbox. Then it came to me to try and pair my old controller with my Xbox as if they had never been paired together before. OMG it worked, it turned out that my Xbox and my controller had become unpaired. Don't know how or why it happened but that's all it was is they were no longer paired. I hope that this is the case for everyone who reads this.
SgtShadow