Wireless Keyboard won't stay on.

I just bought a new iMac at an Apple retail Store. I got the full numeric wired keyboard, and because it is available online as a free upgrade they didn't charge me for it. The wireless keyboard was included in the deal. I want to be able to use it with my iPad and MacBook Pro. When I turn the keyboard on to pair it with another device, the green power light glows for about a second and goes out. No flashing and it doesn't stay on, so I am assuming the keyboard is turning itself off. Neither device can see the keyboard while I am pairing. I have replaced the batteries and am wondering if it is defective or is there something I don't know about. Thanks.