Is this Apple Refurbished? In that case you have full warranty.. and phone support?? ask and see if Apple will help talk you through the setup.
Or is it sold through some other outlet.. and who did the refurbish?
Are you trying to extend wireless of another Apple router?? If so the Express should work.. if not it never will. Apple routers can only extend another apple router.
Failure of the setup often happens with more complex setups.. it is generally better to do it as simply as possible and then adjust the settings..
So for extend wireless from an Extreme or Time Capsule.. I would place the Express right next to the router.. power it on.
Do a reset and then see if you can configure it again.. if not do it manually via ethernet .. is that possible?
Also note the 7.8 firmware on the Gen2 Express is pretty bad.. it causes multiple issues for many people.. I would downgrade it to 7.6.9 or even 7.6.8 but you need it working to do that.. and that is easier done running it in bridge mode.. with ethernet link to the main router whatever brand it is.