The web server I usually use was apparently blown out by a storm, and will be down for an indefinite period of time.
I decided to move everything over to Hostgator, but it isn't working.
I redirected my domain name on Namecheap to the new Hostgator IP address, and I uploaded all my files to the public_html folder. My files are all php, which my htaccess file permits.
I only set everything up about 40 minutes ago, so it's possible that the issue is just time. However I've looked around and that hasn't come up as an issue for anyone else.
I can't think of anything else I may have done wrong. Any suggestions would be greatly appreciated.