Controllers not syncing with xbox/xbox sync button not working

So last night i was playing games as usual, i ran out of battery so, like always, i replaced my battery pack. My controller wouldn't connect after and flashed over and over. (It flashes fast and slow) I thought it was a controller problem, but i've tried all my controllers. The sync button on my xbox isn't working/flashing when i hold it, i've already changed out the batteries a bunch of times, turned it off and on multiple times and did hard resets. I've also plugged in all my controllers with a cable and neither connects it just keeps flashing. This is the 1st time it's ever happened to me, i bought it new over a year ago. Anyone know what to do? :/