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Do you have removed the paper from the rear of the printer ?
Do you have removed the paper completely ?
It can be caused due to sensor problem ?
No, the printer can be dismantled by the help of service manual, but you will not get the sensor in any store. But, before going for other options, can you tell me, if you have open closed the back cover few more times and did you have hard reset the printer ?
There is no button, just unplug the printer without turning off it and then, wait for 10 mins. and then turn on the printer.