HP Deskjet D2300

Please can somebody help me. I can't print from my printer because the green 'on' button constantly flashes, and a warning message appears to say 'cover open'. The cover is *not* open. I've tried sellotaping it down - no luck - uninstalling the software, and reinstalling it - no luck - changing the printer cartridges - makes no difference - taking the back off in case something is jammed - there isn't. Even shouting at the printer that the blankety-blank cover *is* shut makes not a jot of a difference. Does anyone know how I can 'tell' my printer that the printer cover is definitely, irrefutably, *shut*!!!