I have a 95 Altima. It worked fine until one morning I went to start it and got nothing. No horn, no lights, nothing at all. I assumed it had to be the battery but I got the battery tested and I was told that the battery was fine. Does anyone have any clue what the problem might be?

Can you hear the starter making any noise? If so it could be that. Is the engine turning over? You may need to take it to a mechanic and have them run a diagnostics check on the systems unless you know how to make the cars computer flash out a code that you can reference in a repair manual that you can get an auto parts store. It will tell you what system is affected but not specifically which part of the system. That you'd have to track down physically. Good luck. Reckon there's any gas in it?

Check all underhood fuses and links, look especially for a blown battery link.
Also make sure batt cables are clean and tight at battery,grounding point and starter.