Been hacked and the affected website will not even load, you are just presented with a blank page.
- Check that index.php exists.
- Check that inded.php only has the very small amount of standard lines that come with WordPress.
- Check that index.php is not 0 bytes long.
Go in to the Dashboard and install WordFence, the free version is going to be good enough to get you started.
Run WordFence and only if you know what you are doing start making the changes WordFece suggests.
I have found bad index.php files in a number of locations, such as ./cgi-bin/index.php