safari wont open on iphone 4

tried to restart

http://support.apple.com/kb/HT1430

Did you already try to reset the phone by holding the sleep and home button for about 10sec, until the Apple logo comes back again? You will not lose data doing a reset.

If this does not work, set it up again as new device, if necessary without using the latest backup, in case it contains corrupt data.

How to back up your data and set up as a new device