Envy 23 screen not responding

[Alan4908]

I have replaced the cooling fan on this computer and that is all. On refitting the back and trying to start the computer this screen is  initially Leigh showing a little bit of white speaking and 1 centimetre diameter ghost spots which randomly appear and disappear. After a few minutes this settles down but the screen does not respond at all correctly to the keyboard mouse or touch and it's impossible to get beyond the the password entry page. The keyboard produces no effect, the mouse changes from pointer to text cursor as it floats over the password box but what the the computer does not respond to any clicks. Actually it does respond, but very erratically and the mouse jitters as if my mouse is controlling the pointer and another mouse. 

Apart from being noisy the computer was working perfectly before the fan was changed.

Any guidance on this would be very much appreciated thank you very much

[Alan4908]

Just three more pieces of information -  the date icon in the bottom corner of the screen is jumping up and down the screen is first started.

Spuriously the on-screen keyboard  flashes into view and then disappears within a fraction of a second every now and then.

Removing the plastic cover from the back of the screen makes no improvement the same effects still exist even when the computer operates with no plastic cover.