When I returned to my car, I went to start it and nothing

Overall, my car has been driving fine. I've never really had any major issues with it, certainly nothing that did not allow me to drive it. I drove to a friends house from the grocery store right down the street, parked and turned off my car to help her inside with her things. When I returned to my car, I went to start it and nothing. My head lights, dash lights, radio came on with no problem, but when I turned the key all the way to start the car, nothing happens. The car does not even make a sound. It doesn't attempt to crank whatsoever. No clicking, nothing.

It's important to mention three things that have been weird about my car lately. First, practically since I bought the car, I have had a weird problem where all the lights in my car would periodically flicker violently. This problem was always alleviated when I installed a brand new battery in the car. I have always simply attributed this issue to me needing a new battery.

Second, recently (in the past year or so) my engine has been seeming to run "rougher" than usual. The car's idle is much louder than I remember, in fact, so loud that I can barely hear my radio unless I'm on a high volume. The engine's "sound" while running gets even louder when I accelerate. The entire car vibrates very loudly.

Thirdly, I noticed 2 summers ago that my car's temp has been much higher than I remember it. The temperature gauge needle used to sit just under the first line and now it sits on the line or slightly above it. I also have had overheating problems (only during the summer and I do live in Las Vegas). The car would overheat if I was idling too long with the air conditioner running (like waiting at a red light or in stop and go traffic). Sometimes, the car's temp would be just fine until I turned it off, ran into a store real quick and came back and started the car minutes later at which point the needle would be in the danger zone for a moment and gradually go down returning to its usual place on or slightly above the first line.

I don't know if these issues have ANY thing to do with why my car suddenly does not start after running seemingly fine all this time but I wanted to mention it just in case there is a connection somehow.

Please let me know what you think the issue may be and how I can go about fixing it myself if possible. My husband is not a savvy mechanic but he can do quite a bit especially if properly instructed. If need be, I have a mechanic I can take it to, I'm just trying to find the least expensive way to fix this problem in light of my husband's recent unemployment.

Thank you!