Hi shlomo12,
I can't say I have the fix to your problem but I carry my C905a in my jeans pockets all the time. As you know pocket lint is notorious with jeans. A lot of the time some particle is blocking a sensor or keeping something obstructed. So I have to use canned air to blow out the data port and the lens cover.

Take your phone and flip it lens side up. Then slowly slide the door open. Once you see the second lower half of the lens cover lower down, push it down with your finger and use the canned air to blow that whole area out. Then slide the lens cover shut. Then try to activate the camera. See if that works.