Wireless keyboard won't pair after changing batteries

Hi all,

I've been searching through the forums for this quesiton - a lot of people seem to have the same problem - without finding a straightforward solution. Probably because there isn't one.

The other day I changed the batteries on my Apple Wireless Keyboard (two battery slots). It's run on an 2011 iMac with OS X 10.9. Immediately after the change some keys stopped working, whereas certain buttons seemed pressed down 'xxxxxx....' making it impossible to continue using the keyboard. So I tried to reset the Bluetooth pairing. In the beginning it worked to some extent, but the first problems always came back. Now I can't pair the device- it gets detected, and I start writing the passkey, all digits usually work, but the 'Return' key won't respond. Thus, the keyboard won't match. Suggestions? Is this a hardware problem? Seems improbable since it started happening once I changed the batteries?

All the best,

Dag