Well if you are 'sure' it is charged, but it is only turning on to the Android logo.. try this and see if it will let you in...
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.
Once in "Safe Mode", if it lets you in, then you need to check what app/file is causing your device to not work correctly and remove it.
If that doesn't work, then you may have to do...