how do i switch on my iMac bluetooth it is not working, the icon on top menu bar is in light grey?

I have tried turning bluetooth on and off and removing keyboard (which wasn't connecting) it then found it but wouldn't pair with it, and then I removed the iMac (as it said it wasn't connected either, although the trackpad is connected, the icon on top menu bar is light grey with 3 dark dots across the middle, rather than being all dark grey. Now I can't seem to add the iMac back on to the bluetooth menu and I am wasting heaps of very precious time trying to sort it out!!

Somebody please help me!!