Generic firmware error
Try the following:
1. Switch the power off from the back of the printer and disconnect the power cord. Reconnect the power cord and power on the printer.
2. Check that the printer has the latest firmware version. If not, update the firmware to the latest version.
If you see system error 79:04, see Appendix A: How to troubleshoot SE 79:04.
A firmware upgrade will not always solve the problem. The best way to solve this problem is to report the error to HP correctly. Make sure that you supply all the information accessed by pressing the Up and Cancel keys together while viewing the system error screen, or preferably provide the printer log and diagnostic package to HP.