I can ssh into my EC2 webserver instance, but my site is down

I'm new to AWS and web development, and I'm running into a strange issue. I'm hosting my website on an EC2 free micro instance with httpd installed, and I can ssh into it and push html code updates to it with SFTP just fine. I've been pushing up code and ssh'ing in and it's all working.

Except my site is completely down all of a sudden, and I didn't change anything with httpd. My ELB shows the EC2 server is OutOfService, and I can't get any page to load (I've tried both the URL and the EC2 IP address). I've tried rebooting the EC2 instance and still nothing.

What could the issue be, and how could I find out what the issue is?