I rebooted my iMac yesterday and it refused to accept my login password even though I was certain it was correct... arghhhhh.
After searching the Apple Support Communities on my MBPro for a solution and finding nothing I decided to try the Command - R option on restart and then use Utility - Terminal - resetpassword even this did not work but I did notice that the information I was typing in was double the length of what I was actually typing... strange.
I now tried my (wired) keyboard on another iMac that did not require a login password only to discover that for every letter I typed the keyboard was 'tagging' it with a spurious 7.
Ordered a new keyboard from Amazon this morning even though I have two Apple Stores within a 10 mile radius and it is coming tomorrow. Even better as a genuine Apple keyboard it is £10 cheaper than Apple and I get free delivery.