Bluetooth Issues

Recently my iMac has been taking a few minutes to recognise that it actually has Bluetooth technology built into it... which is extremely frustrating since I use a Bluetooth keyboard!
When I first start up, the Bluetooth icon in the menu bar says "Bluetooth not available" and then after a few minutes it comes on without a word. It's not that it's taking a while to find the keyboard - it's the actual Bluetooth hardware it can't find.

Has anybody encountered this before, and found a fix?

-how is the rf signal strength from the keyboard
-pardon me for saying but replace the batteries in the keyboard
-delete the keyboard pairing out of the mac, re-pair mac to the keyboard

how does the keyboard behave on another mac (field trip to a mac store)
is there a stuck key on the keyboard.
will the mac do bluetooth with another device say a cell phone

As I said in my original post, the keyboard is not the problem. It's the hardware in the computer - it doesn't recognise that it has bluetooth in it.