MathiasVDA:
I'm not sure if it's related but try placing a delay between entering the PIN and attaching gprs. Don't try to do them together as I found out here:
GPRS connection problem - Arduino GSM Shield - Arduino ForumAs for your second question, by press and holding the button for a couple of seconds, you turn off/on the shield
It Worked! 
Thank you very much!
They should solve this issue.