Im trying to conect my keyboard to the imac, so on the screen says "To pair a bluetooth keyboard, turn it on and wait for your computer to connect to it" so my keyboard is on but I don't see it connected, anyone can help?

Please read and follow the instructions below:

The following will require any USB keyboard an mouse. If you don’t have them, borrow or buy them, they are inexpensive!

1.     Connect the USB keyboard and mouse to the computer.

2.     Open System Preferences – Bluetooth

3.     Un-pair the wireless keyboard and mouse.

4.     Turn off Bluetooth

5.     Restart the computer in Safe Mode per the directions in https://support.apple.com/en-us/HT201262

6.     Restart the computer normally.

7.     Open System Preferences – Bluetooth

8.     Turn on Bluetooth

9.     Re-Pair the wireless keyboard and mouse.

10.  Unplug the USB keyboard and mouse and begin testing the wireless devices again. 

You might also check the batteries in the keyboatd.