Do any of your other apps work or is it just Safari that's giving you the grey screen?
If all else fails, a reboot is called for. Hold down the Power and Home buttons for a long time (could be up to 20 seconds) until the white Apple logo appears - have faith, that logo will eventually appear. Then the iPad will reboot - again, it takes a while, so be patient.
Then you're back to normal and it's all no big deal.....