Hi, welcome to iPF!
There are a few things you could do:
Reset your iPad by pressing and holding Home and Power button until the Apple logo appears. You won't lose anything when you do this.
Turn off 3 G on your iPad and on again. Perhaps it will "come back to life".
Second kind of reset (you'll lose network settings when doing this): go to Settings - General - Reset - Reset Network Settings, then set up your network again. Try this a few times, if it doesn't work at first.
Backup your iPad, reset all content and settings and set it up as new.
If all these suggestions won't help, contact your provider. The problem could be caused by them.