Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
The Cover is Open message will appear if the printer thinks that the top cover of the machine is not closed completely.
To clear the error message, make sure that the top cover is completely closed.
Open the cover, then close it again firmly.
If the problem persists, try keeping some pressure down on the cover whilst trying to print.
If that doesn't work, then the little plastic part that triggers the cover sensor may have broken off.
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There should be a little plastic protrusion on the cover that fits down into a slot on the main body of the printer - if it has broken off then the sensor will not be triggered.
Look for the slot on the lower part of the printer where the lid meets with it and check if there is a matching plastic protrusion on the cover.
If there is not then you can try to jam the sensor with something.
Ok, can you try jamming the sensor anyhow? It may be that the sensor has slipped lower down and the plastic piece is not touching it.
Yes that is the sensor.
It needs to be pushed fully down by the plastic piece on the top cover.
Ok, then it seems that the sensor has failed - if that is the case then it will need to be replaced.