I have an Apple wired keyboard and a wireless Microsoft keyboard. I have been working with the Apple keyboard for a couple of months. Today I started my iMac and it didn't recognise the keyboard, I plugged the Microsoft keyboard (I worked with it for a year before I had the Apple keyboard) which works via USB (but wireless) and the iMac did not recognise it either. I tried the SMC reset, as shown here but it didn't work.
Any idea of what's happening? I appreciate your help.