iPhone 4 won't turn on and unable to continue with your activation at this time

I have an iphone 4 which was working fine. I tried to update it but this time I used a computer running xp. When I did so I got an error. Since getting this error my iphone will not turn on. I am not even getting apple logo. It does show up in itunes but I get the message:
"We're sorry, we are unable to continue with your activation at this time."

I have tried holding down the home and power button to do a restore and nothing is happening. Please help! Thank you.