If the connection between your printer and computer breaks, then error code 40 occurs in the HP Printer, and then you cannot give any print command. You can resolve this error by implementing the following steps:
● Check whether your system and HP printer have the same baud rate.
● You can try to reset the network by turning off the HP Printer.
● Make sure that all the printer cables are connected with right Enhanced Input/Output ports.
● Even check that the EIO is seated correctly or not, and nothing is disturbing it.
● Serial configuration of your printer should be the same as that of the system.
If you have any difficulty while resolving the issue at hand, then you can call HP Printer Helpline Number that is available at all hours.

Also Read: How to reinstall HP Printer Drivers