cannot get wireless keyboard to stay turned on
I have been trying to get my wireless keyboard set up, but it won't stay turned on. I have replaced the batteries and tightened the screw, but the green light stays on for just a couple of seconds and then turns off and my computer cannot find it. Am I doing something wrong that I don't know about? It's a 2009 Aluminum Keyboard with center antenna.
Any help would be appreciated .
Mac mini (Mid 2010), OS X Mountain Lion