Iis – Allow incoming connections on Windows Server 2008 R2

Good day people.

First, im new to Windows Server. I've always used Linux/Apache combo, but, my client has and AWS EC2 Windows Server 2008 R2 instance and he wants everything in there.

Im working with IIS and PHP enabled as Fast-CGI and everything is working, but, i cant see the websites stored in it from internet.

The public DNS that AWS gave us for that instance is:

http://ec2-XX-XXX-XXX-121.us-west-2.compute.amazonaws.com/

But, if i copy paste that address, i get nothing, no IIS logo or something like that.
My common sense tells me that maybe the firewall could be blocking the access.

Can anyone help me and tell where to enable some rules to get this thing working? I don't wanna start enabling rules at random and make the system insecure.

If you need any additional info, you can ask me and i will provide it.

Thanks in advance.

UPDATE:

Amazon EC2 display this:

Public DNS: ec2-XX-XXX-XXX-121.us-west-2.compute.amazonaws.com
Private DNS: ip-XX-XXX-XX-252.us-west-2.compute.internal
Private IPs: XX.XXX.XX.25

In my test microinstance, i just to use the Public DNS address (the one that starts with "ec2") and it works like a charm (of course, the micro instance have its own Public DNS im not assuming same address for both instances…)

However, for the large instance, i tried to do the same. Set up everything as in the micro instance but if i use the Public DNS, it doesnt load anything.

Im suspicious about the Windows Firewall, but, the HTTP related stuff is enabled.
What should i do to get access to the large instance? I don't want to set up the domain yet, i want access from an amazon url.

2ND EDIT: all fixed.

Charles pointed that maybe Security Groups was not properly set up for the instance. He was right. Just added HTTP service to the rules and all works good.