Once I bought my car I gave it a major tune up. But recently when I drive it for a while during the day it gives me a weak start up, and a couple weeks ago it didn't turn on at all. It wasn't the battery or alternator, I even changed the main relay on it and nothing. Im getting the same problem, that annoying weak start up. Help!

Remove and fully charge the battery. Most auto parts stores will test and charge batteries for free. If the problem persists, the starter may be bad.

My battery is brand new.. about a week old.