Hi @Ketchyfilms,
Welcome to the HP Support Community.
Thank you for posting your query. I will be glad to help you.
I understand your HP Envy Photo 7858, is stuck on a screen where you are not able to use it even after try to reboot the device, Sorry to hear about the trouble, Please try the Hard reset one more time keeping the cartridges out of the Pc and let me know how it works.
Please remove the Cartridges from the Printer if possible, and try a Hard Reset. Do keep us posted to help you better.
** Hard reset :
1. Turn the printer on if it is not already on.
2. Wait until the printer is idle and silent before you continue.
3. With the printer turned on, disconnect the power cord from the rear of the printer.
4. Unplug the power cord from the wall outlet.
5. Wait at least 60 seconds.
6. Plug the power cord back into the wall outlet.
NOTE: HP recommends connecting the printer power cord directly to the wall outlet.
7. Reconnect the power cord to the rear of the printer.
8. Turn on the printer if it does not automatically turn on. The printer might go through a warm-up period. The printer lights might flash, and the carriage might move.
9. Wait until the warm-up period finishes and your printer is idle and silent before you proceed.
HP Smart App: Please uninstall the HP Smart app --> restart the Device, Wi-Fi router and printer --> reinstall it back and add the printer.
HP Firmware Update: Please update the Firmware from the link. This will help to update the firmware on the printer or devices.
I hope this helps.
Take care and have a good day.
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VikramTheGreat
HP Support