iM 4,1-14,4 Mac won't complete startup

[davidprestidge]

We have a fairly elderly Mac Intel my wife uses. It normally just starts up fine, with no password needed. Now, this happens.
Goes through the normal grey screen, and progress bar.
Then it shows her name, and requires the password. You can see a blurred version of her desktop image in the background.
USB Keyboard is dead, so impossible to input letters, except the F1/F2 (brightness) keys register as dots in the password box, but no letter keys work
I have tried a NVRAM reset - no joy.
Any ideas, please?

 

[Fishrrman]

This may or may not help, but will it boot with a "safe boot"?
(hold down the shift key CONTINUOUSLY while pressing the power on button, and as it boots)