Error message 5100. cartridges wont eject either

Solution 1:
Clean the timing strip.

Solution 2:
The purge cap (the white sliding mechanism that the print head parks to when it's not in use) may be not lubricated well enough .

Lubricate the sliders with some white grease (don't get it on the small wipers or the black caps); this repair probably require to remove the right panel off of the printer to gain access to the purge mechanism.