iphone won't turn on past apple sign...

I turned my iphone 3g off about 3 hours ago as during a phone call I got cut off and it said 'no service'
When I tried to turn it on again, the apple sign would just appear but just stay like that, it won't turn on!!
From time to time it will flash a white screen but then go back to the apple sign.

I can't sync it to itunes either to do a restore as it won't recognise it when I plug it into the usb.

Any ideas on what I can do, or do I just have to get a replacement?

Thanks in advance!!