my phone freezes when its turned on?

i got the sony ericsson W910i at christmas, and not long after dropped it in water. it dried out fine and everything was working normal.
about a week later i started experiencing the normal problems with this phone that people are complaining about (switching off, games not working) but i found my way around that. the games arent working or the applications but everything else is.
it still switches off though.
i think when i dropped it in the water, it damaged the internal battery as it's always saying its low on battery even when its fully charged.
the most recent problem is the biggest!
i had it on my bench and the screen lit up. i went to see why it lit up to find that it had froze. nothing was working!
i took the battery out and turned it back on. when i did it got as far as the main screen when you turn it on, it said 'searching' where 'vodafone uk' normally is, and then it freezes again, completely locks off.
is this something to do with the water, or is it a problem other people are having?
what's the best thing to do if i want a repair?