What do you need to fix? If you enabled mod_rewrite but you have no rules in your .htaccess file, then the host will act like it was before. It doesn't change anything by itself. Plus, when using mod_rewrite you NEED to have a goal. That's why you enabled it in the first place, to do something with it, not to just have it there...right?
I have optimistic thoughts, even though sometimes (if not always) life's a bitch.
You might not have rights to change Options in your .htaccess. Confirm with your sysadmin that 'AllowOverride Options' is set for your virtual host. Then try removing everything from your .htaccess but the following (same as Kalle said, minus any rules):
If you have that in your .htaccess and you get an internal server error, then mod_rewrite isn't properly enabled in Apache. Your sysadmin needs to uncomment the following line and reboot the server: