I am sure your battery is not too old. And I hope you are using a good anti virus software for your phone.
If your phone's battery is ok, the next thing that we need to make sure is that your phone is not infected by any virus or worm, common symptoms of infection are non responsive blue-tooth, slow performance, unstable operations, etc.
There are many anti virus softwares available for your phone like Symantec mobile security. Download a trial version and install it on your phone, run the live update (requires gprs/3g internet access) and run full scan.
Another work around would be to format your phone's internal memory which you can do by pressing *#7370#. Please remove the memory card before doing so. Also make sure the battery is fully charged. In your case, plug in the charger before proceeding. Format the memory card as well through a PC before using it on your phone again.
I hope this will help...