Maybe the battery. This happened to me and when I took it to Pepboys they recharged it for 2 hours and after that battery was still at 75%. Hopefully, thats the issue with yours. It sucks leaving the radio or dome light on coz if your battery is already weak to begin with, rest assured the next day its drained.
Make sure the battery terminals are tight and do not move when tight. Sometimes they can stretch and cause a huge voltage drop because of a bad connection, or may not allow any current to flow at all. Hope there are no further problems.
If the starter is ever suspect, and will not turn engine check the "S" terminal on the starter solenoid for proper voltage while turning key to the start possition. If there is good, near battery voltage check for available voltage at the "B" terminal on the solenoid while starting. You should see battery voltage, if not there is a large voltage drop in this wire most likely due to corrosion and needs to be replaced.