Yes, you would normally connect the 0V rail of one circuit to the 0V rail of the other circuit.
Try just connecting the 0V rails together. If this causes a problem, the two circuits were not completely isolated from each other, so you need to fix that. If the problem only shows up when you connect the +5V power rail from one circuit to the other, there's probably a power supply short on the second circuit, or perhaps you're connecting it with the wrong polarity.
You're asking a lot of vague questions. It's really difficult for us to know how to answer when you don't give any background information. You sound like a beginner, and there are so many mistakes that you might have made that it's hard to know what to suggest first.
You need to start by describing the whole project, any special components that are used (e.g. ICs, modules) (with full part numbers, and preferably, links to data sheets), then post complete schematics.
Also, this discussion is not related to the first part of the thread. You have hijacked someone else's thread. I (or another moderator) will move this discussion to a new thread once we have enough information to decide what the name of the thread should be.