If you go to www.ipchicken.com
, what does your systems IP show? What is your ISP providing you with, dynamic or a static IP address? Once you have your IP address (the one the world sees) can you type it into your browser and get any results? You should see one of two things:
1) Default Apache Screen (index.html)
2) Your web site
First thing I would check and like the others said is your router fire wall, make sure that port forwarding is set to the right ip address. On that note, have you assigned a STATIC IP address to your web server? If not your router could be assigning a different IP every time you reboot. I am willing to bet, at least from my experience that you may being using DHCP on your server rather than a static.
Your setup should look like this:
ISP (IP: 100.100.100.99) --> Your Router (IP: 192.168.1.1) --> To your server (IP: 192.168.1.50)
Static/Dynamic --> Port forward 80 points to ur srv --> static ip on your server
PM me if you need help or e-mail me
Hope we helped in someway!