Still, sounds like moisture damage.
Not to argue, but do you know how many users in this forum with over 300,000 members and 1.2 million posts we have seen with similar issues, come to find out it really is moisture damage. Note, I did not say your BB got wet, I said moisture damage.
That could come from a very steamy bathroom during a hot shower, which is why I said take the battery and out and follow the suggestions in the link. IF it is moisture damage, leaving the battery in only adds to the issue IF it is moisture.
If it's not, then you're still safe.