Hi MN77Aust,
Μy apologies; I have realized that an external monitor may not work.
From the symptoms above, it appears to be an issue with the display of computer and need replacement. If the computer is under warranty, you may private message me the service tag of your computer. I have added you as a friend. Please accept my friend request by clicking on my name highlighted in blue and then click on “Friends” tab at the top and then click on “Request to Review” and finally click on “Accept” button.
I am sending you a private message as well. Click on “Inbox” to respond to the message and provide system’s Service Tag and contact details so I may access your system records and check for further course of action. You could also click on Start Conversation to send a private message.
Please reply with information.