Can you tell us if anything happens when you try to turn it on or does it stay blank?
You probably have a hung application so can you press and hold down the power and the menu buttons for a full 15 seconds, during that time the phone should power up then shut down then power up then shut down again.
After it has shut down the second time can you then press the power button for 2 seconds to see if it will power up cleanly.
If not can you do the same thing again except do not power it up, Instead can you open iTunes then connect your phone to the machine and see if it prompts you to recover the phone.
Let me know what happens
Glad you got it sorted out