Did you try this
Make sure that the power is turned on, then, holding both sides of the paper output tray, gently open it.
- Lift the operation panel and open until it stops. The print head holder moves to the replacement position.
According to the operating instructions error 5100 indicates that there is an obstruction - possibly due to packaging.
Have you followed the instructions as detailed here. If you scroll to the top it shows you step by step instructions about getting the printer head to move to put in the cartridges.