K800i problems!

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Please can someone help??
I have the Sony Ericsson k800i and never had a problem with it until today. For no reason, the screen went white then turned off. When i turn it back on it just freezes at the start up picture and goes no further. It's fully charged and i have only had the phone for 2 months. Is there a simple solution or is it a case of sending back to 02 online?

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Don't know if this helps anyone trying to help me, nut the phone works without a sim card in it.