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Check in your printer's settings: see to it that
in Options is set to
Use Printer Settings
Otherwise, you may quite simply have one of a number of hardware failures in the Tray A area: a defective sensor, operating cirucitry, etc.
Try setting the tray to another tray or the manual feed slot (if there is one of either), on both the printer, and in the printer's driver settings on your computer (and also in any software program you print from, if it has printing settings of its own.)
Driver settings (if you have a Windows PC) are found, for a printer, in
Control Panel - Devices and Printers
and right-click on your printer's icon there, and select Properties... those are the 'driver settings' for the printer. (Be sure to save the changed settings by clicking on OK until all Properties sheets have closed.)