My Car Won't Start After Buying New Parts For It

One day as I was driving I came to a stop and noticed that my car started puttering pretty noticeably. I got the oil changed soon after but even after it still continued. It started to have a hard time getting the car started so I replaced the battery and had no troubles starting afterwards but it still continued to putter. Soon enough it started having a tough time catching again when I would turn the ignition so I replaced the alternator. A couple of weeks later it started having a hard time turning on again. Eventually it would not start up anymore. I figured it was the cold weather but from everything I was hearing and reading I came down to the conclusion that I would be replacing the starter at the end of it all, so I did. One day later it would not start up again. We ran a computer on it and pin pointed it down to one of the relays on the main panel underneath the dashboard. We noticed that it would not make a cranking noise as if it were to turn on, in fact it made no such noise. From the relay panel we noticed that the bottom right relay was making a grinding noise upon turning the key. I replaced the relay, re-adjusted the battery, turned the key and it cranked for one second and then died off. I tinkered around but it went to making only the grinding noise from the relay.