Michael Spearin, disassemble your iPod following the manual on here. Take a look under the click-wheel, the select button is the center button. You should see 5 micro-switches on your logic board corresponding with the click-wheel. On the switches should be little black round rubber "bumpers" Those have a tendency of slipping of the switches and thus your button may not make proper contact with the switch. To replace or repair those, I do get round felt with double side tape from Walmart. They sell it for the bottom of furniture legs. See if that works for you. The other thing you can check while you have it apart is the switch itself. Just push on it and see if it "feels" like the other ones. If it does not, you may have to replace the board. Good Luck and let us know.
iPod 5th Generation (Video) Click Wheel Replacement