Hello, welcome to JustAnswer!
From what you've described, it sounds like the undo function of Control - Z is being called when you press the Z key.
Does this happen in all applications?
Have you tried connecting another keyboard to your iMac?
If you still require assistance, please reply back and the system will send me an alert.
the z letter seems to be working now.tried other apps and the z is functioning in all.
I'm glad it's working now. If you have any other questions, feel free to ask. Have a good day!
is this a common problem?what happens to cause this?
It's definitely not common. It's hard to determine what would have caused that. Maybe the application you were using had a glitch at that time. When things like that happen, its probably best to perform a shutdown/restart of your computer.
ok thanks for your help toby