iPhone 3GS, Power button works but wont shut off???

as the title says i have a iphone 3gs, and the power button works when i press it but when i hold it to power it down it doesnt work. i tried searching for anyone else with this problem but cant find anything.
anyone know whats going on or how to fix it?
thanks

Try connecting it to itunes and restoring. Or just hold power button and home button for 10 seconds to reset it. See if that works.

New MBP User said:

Try connecting it to itunes and restoring. Or just hold power button and home button for 10 seconds to reset it. See if that works.

Click to expand...

The key is not the 10 seconds, but until you see the Apple icon on a black screen. I've had this take up to 15 seconds on occasion.

I'd also try the reset, this should not cause any data loss - it has't on mine.