You are describing symptoms of moisture exposure. From what people report, it sometimes doesn't take much. A sweaty pocket. Fogged up shower room. Someone even thought condensation when leaving an air conditioned space to the humid outdoors was causing problems.
See
BlackBerry FAQ - BlackBerryFAQ and the article on what to do if you get your blackberry wet.
If you don't think moisture is the problem, and the device is under warranty, don't delay, contact customer service where you purchased it and go from there.