Robots Will Kill
Few things you can try:
1. Go to "Settings" then "Accounts and Sync">Manage accounts>Gmail account>make sure Sync Calendar is selected.
2. Go to "Settings" then "Accounts and Sync" and make sure that "Background Data" and "Auto-sync" are checked.
3. Go to calender settings in Gmail from your computer and verify your phone number under calender settings mobile setup.
4. Add another google account to your phone (make a new one if you don't have one -they're free) and set it up to sync everything. You can delete it again once the process of adding it has reinstalled the missing sync drivers.