Q: Keyboard not restarting after changing batteries?

Hello Mrplip,

It sounds like your keyboard is not starting after installing new batteries and are unsure of how many batteries you need for your keyboard. This article will help you determine if have the correct amount of batteries and orient them properly when you insert them.

Apple Wireless Keyboard, Mouse, and Trackpad: How to install batteries

http://support.apple.com/kb/ht3903

And this info should help you troubleshoot the keyboard not turning on:

Keyboard

• Push and release the On/Off switch to turn on the Apple Wireless Keyboard.
• When your keyboard is on and paired, and the batteries are charged, the light will glow steadily for several seconds, then turn off.
• If your wireless keyboard isn’t paired with your Mac, the indicator light will begin to blink. This indicates your keyboard is in discovery mode and ready to pair with your Mac.
• If the LED doesn't light up, remove the batteries to make sure they're good and that they're installed correctly.

Note: If the battery compartment cover is not installed properly the On/Off switch may not function correctly or may be difficult to operate. Remove the battery compartment cover and carefully reinstall it.

 

From: Troubleshooting wireless mouse and keyboard issues

          http://support.apple.com/kb/ts3048

Thank you for using Apple Support Communities.

Take care,

Sterling