Will not Take Pictures, Lens possibly damaged

Is the lens sticking out at all? does it look square to the body? the front has a square opening is it square with the rest of the camera? Some times a weak battery can cause this or debris in the gears of the mechanism. Sometimes tapping on the unit while powering it on can free the lens and it will function. Sometimes a fresh charged battery will also work. It sometimes can take a bit of power to get it over the jam. Have you dropped it or banged it recently? have you shot in a dusty enviornment latley? sand, dust wind? these conditions can cause problems.

Just wanted to say that the tapping method actually worked! My Powershot SD450 was in a dusty/rainy environment and the screen didn't make any kind of jamming noise at all... just wouldn't open when I turned it on, the camera beeped five times and shut itself off (I have a cracked screen, so I couldn't tell if there was an on screen error). I tried tapping and pressing on the lens area while powering on and after about 10 tries it worked. I ended up opening the camera and trying to dust it out as well. Just wanted to say thanks BowerR64