It's just unable to start due to something missing or broken. Don't panic, there's no issue. I did this the day I got my phone, and there was nobody to "help" as such, so I just fixed it myself.
These are the steps to fix a boot loop. If you do this correctly, it WILL fix it. But you must do it EXACTLY to the letter.
So here we go...
1) Turn off your phone. Unplug it from your computer etc
2) Hold down home, power, and volume UP. This will enter recovery mode. If you are using CF-Root, you'll get CWM recovery. If not, you get stock recovery. It doesn't matter which appears.
3) Choose to wipe user data from the menu.
4) Turn off the phone by long-pressing the power button.
5) Prepare ODIN on your PC by using task manager to kill any KIES processes, then open ODIN.
6) Put your phone into download mode (home + power + volume down)
7) Plug your phone into the computer using the factory USB cable. The leftmost box should go yellow and an ID number will appear.
8) Flash a stock ROM from those available in ODIN format, and the phone will boot correctly.
Alternatively, it is possible to flash VillainROM 1.1 if you are not comfortable in wiping via recovery, or if you cannot do so for any reason (corrupted kernel etc), as it wipes all users data when installing. Simply ignore steps 2 to 4, and flash VillainROM 1.1 via ODIN instead of the stock ROM.
Any questions about boot loops? Ask them here rather than making new threads.
Adding a nice little video from user "dullah"