The Nokia 5233 needs to be master reset to the factory settings every so often to give the phone a fresh start. Sometimes if your mobile phone has any bugs or freezes up, hard resetting can usually fix the problem. If you still face problems with your firmware trying updating the it using Nokia software updater. Make sure when you hard reset your phone, you back up all your important contacts and messages, using Nokia back up software. You can use this reset method for all Nokia phones running the symbian operating system such as the 5800, x6, n95 etc..
To reset your device simply turn on the phone and enter the full reset code which is *#7370# into the phone's keypad. Now confirm to reset the device and wait for your mobile to reset itself. Make sure you remember to restore all your back up content you made using Nokia software.