Have you tried completely powering the NT off by holding the power button down? This sounds like a memory error to me. Android devices are not really efficient at freeing up memory resources after a lot of use and most of us just let our NTs go to sleep and don't power them down once in awhile.
You may also want to clear browser caches, histories, cookies, and so on periodically.
Powering down will stop background processes that may be running.