SE K850i O2 keeps switching itself off and now won't turn on

Hi,
    anyone else had a problem with the K850i. Mine started about a week or

so ago, when I noticed that my phone had switched itself off.
    At first it was a minor irritation, but over the last couple of days
it 
has got worse.


This evening it turned itself off and now won't turn back on. I've tried 
removing the battery, etc.
I know it was charged up, so it wasn't that!

So I phoned O2,  the person I spoke to admitted there were some problems 
with the model but mainly to do with texting.
anyway  I now have to take Tuesday off as an annual leave day to wait in
for 
parceline to come and exchange with  another one.

Will not allow an exchange at my workplace,

Andy