Need help… WordPress don’t run

My wordpress crashed.. Need hint about the problem and how to fix it.

I got error message like this when trying to access the website :

Parse error: parse error, unexpected $ in /home/content/t/a/n/tantam/html/index.php on line 18

I also get error messages like this when trying to access the wp-login
to get into the dashboard :

Parse error: parse error, unexpected $ in /home/content/t/a/n/tantam/html/wordpress/wp-includes/default-filters.php

I try to uninstall the wordpress and reinstall it.
The problem seems to be fix and the wordpress running smoothly again.
But after 3 days the problem come again. And I got the same
error messages like before.

I’m a newbie with wordpress. I really appreciate for the help.
Thanks.