If your phone is having issues at start up the problem could be related to a corrupted file, a corrupted Android OS, or a hardware issue. There are a few ways to troubleshoot this issue:
1. Remove the Battery
I always recommend removing the battery and leaving it out for 30 seconds. This clears the RAM cache and may resolve your issue.
2. Soft Reset
To perform a soft reset, press and hold the "volume down" and "power" buttons simultaneously for 15 - 30 seconds. This works on most Android devices.
3. Remove Connected Peripherals
A faulty SD card or any other accessory (such as a headset/headphones or even the battery) may cause issues such as the one you describe. If possible you may want to buy or borrow another...