The functionality of your site doesn't only depend on you, but also on your webhosting company. They might upgrade their Apache and forget some settings, so your clean URLs don't work anymore.

When you get something like Fatal error. Allowed memory size of 33554432 bytes exhausted... (normally when you activate new modules), extend the memory resources in the php.ini file in the Drupal root. If it's not available copy it from another Drupal installation.

When clean-URLs doesn't work, first try to go to http://drupal.org/node/121834 and grap the .htaccess rewrites and put it in the .htaccess for your drupal site.

The safest thing is to make your website work also with clean-URLs disabled. Whatever happens, it's not a big deal. To do this you have to:

• make all links in the form of e.g. /?q=node/123 instead of http://yoursite.com/content/title. This offers also the advantage of all links working on an off- or online backup site with another name. If you use the node number, you can change the titles of content without messing up your internal links. Consider that changing titles might lead to dead links in external sites, not leading to your pages anymore.
• install and activate the module Global Redirect. The only thing to change in the settings:
  Case Sensitive URL Checking:
  
  Disabled

  Enabled

When clean URLs isn't working, your site should be working anyway. In case you need to disable it:

• Login with yoursite.com/?q=user
• Disable Global Redirect first. Go to yoursite.com/?q=admin/build/modules. Disable and see how your site is running. This might be sufficient.
• Try to avoid disableling clean URLs. You might not pass the test to enable it again. If you need to do it anyway, go to yoursite.com/?q=admin/settings/clean-urls. Check your htaccess file(s).

Before worrying too much, check the server status at http://serverstatus.bluehost.com

Make a screenshot of your cPanel, just to know if Apache and PHP versions has been changed that can be due to a problem. It's nice when you can call support and tell them that you have a problem after they upgraded something. They will be surprized you keep track of it and sure makes their job a bit easier.