BB Curve :: Screen Just Goes White And That's It The Phone Don't Work?

I have a problem with a curve 8520,I'm on the orange network and two days ago the phone started to play up, for no reason the screen just goes white and that's it the phone don't work, if you remove the battery and reinsert it, it some times only goes halfway through the boot up then just goes white again or will go all the way through, works as normal for a few minutes or seconds then back to white..rrrrrr!!!!Took it into the Orange shop where they tried to do a OS update and all that's done is make it go white halfway through boot up every time.... They then told me that they only cover the phone for 12 months and I've still got 3 months left on the 24 month contract... I believe blackberry phones are covered under a 24 month guarantee.