Neutral joined to ground line
It sounds like the neutrals for the lights and receptacles, which should be all combined (they are) and have one wire going back to the main panel, don't have that main wire working correctly. It could be cut somewhere, but most likely it is disconnected either at the last receptacle or light on the circuit that works or the first one that doesn't work. If NOTHING on the circuit works then it could be disconnected at the panel.

So somebody got smart and said "neutral and ground are bonded at the panel anyway, so what's the difference? I'll just combine them here and everything will work."

There are two problems (aside from it being against code):

1 - There are situations where something could go wrong such that this extra connection between neutral and ground will result in a very dangerous condition, where instead of ground acting as a protection in one location it ends up causing dangerous levels of current to be present elsewhere.

2 - The ground wire is a bare wire (not good for normal neutral) and may not be the same gauge as the neutral is supposed to be. If it is thinner than the neutral is supposed to be then there could be a situation where all equipment is working properly (no short circuits) and the total current is below the circuit rating (15A or 20A) so the breaker doesn't trip, but over time the ground-as-neutral overheats and causes a fire, which is not a good thing. I am not an expert on the code requirements - a quick search shows 14 &amp; 12 gauge for 15A and 20A circuits for ground, which would be the same as neutral. So I could be wrong on this specific problem, provided the ground wire is the correct size, but fix it anyway for all the other reasons.

This must be fixed. Disconnect the ground from the neutrals. If you know the wiring sequence from the panel out to the receptacles and lights, start with the last one that works and check each connection. If you don't know, check them all. If you can't find the problem anywhere then it may be at the panel - in which case you may be better off calling in a professional (which is what I would do - I'm not an electrician and my skills at the cover of the panel).