Error 0x887df78a on HP Officejet

Solution:

1. Take out both ink cartridges and leave them on tissue.
2. Clean both cartridges thorougly with a dry cloth, and dab with tissue
3. The four buttons in a circle with the button in the middle: press it and hold whilst the printer is ON for up to 30 seconds
4. Pull out all trays
5. Put the cartridges back in, put trays back in