Hi I cant log in

Hi

My daughter was playing on the imac last night when she pressed the w key it froze and would not let her continue or let me turn the computer off.

Now we can't log in when switch on and try to put password in it doesn't put in what I am typing e.g. when press the letter Y it puts in hjnuy I have tried 3 keyboards and it happens with all of them.

Does anyone have any ideas. Can't actually get in to use the computer or change any settings, it will let me sign as guest but asks for apple id and password but cant put these in as types gobbldegook!!

Any help would be greatly appreciated

Thanks