Alright mate. What happened? What were you doing prior to that?
Also, does it vibrate or do anything else that makes you think it's stuck there?
How long has it been on that screen for?
Depending on your answer to these questions, maybe I can point out a few things that would work well:
In any case, try these steps (in this order)
Remove the battery and unplug the phone from any power outlet.
Replace the battery and try booting up again. Does it work? Yes, you're done. Else
Remove the battery again. Place the battery back in the phone and hold the "R" key on the keyboard.
While still holding the R key, press and release the power button for abut a second or two to turn on the phone. Do not let go of the R key.
You will enter recovery mode. Use the volume buttons or the directional arrows to wipe cache/dalvik-cache and reboot the phone. Does it work? Yes, you're done. Else
Enter recovery mode again with the R key trick.
Wipe data and restart phone once more. you will at this point lose all data you've added to the phone
Factory reset the phone. Choose that option 3 times for good measure.
Restart the phone. Does it work? Yes, you're done. Else:
Refer to the ODIN thread in the all things root subsection to reset your device to factory settings
Good luck.