Imac wireless issue.

I've had my imac since july last year and up until now it's worked flawlessly.
However, about a month or so ago I started getting the keyboard lost connection error once every 15-20 minutes. It would clear itself up after a few seconds usually.

Then today, I wake my computer from sleepmode and the keyboard is dead. I replace the batteries and suddenly both the keyboard and mouse are no longer responding. Pressing the button on the side of the keyboard makes both flash their little green button but it dies after a few seconds.

Any idea what this could be? And if so how I could go about fixing it?