It sounds like you are very low on memory.
What is your file free Options > Status?
Pull the battery and check again. Post your results back here.
Also, follow these links to prevent this issue from happening.
http://www.blackberryforums.com/gene...ee-memory.html
Why is my BlackBerry losing its call logs or message logs? - BlackBerryFAQ
How do I free up memory on my device? - BlackBerryFAQ