Are your DNS Record settings correct?
Not to be simple, but sometimes it is the simple things which get overlooked, so,...
Log in to your Linode account and go to Linode Manager
go to the
DNS Manager tab.
Scroll down and look at
A/AAAA Records
You will see fields for : Host Name IP Address TTL Edit Remove
The first row of entries has
nothing in the first field - this makes your site
http://example.com show up - and it should have your ip address in the second field of that row.
The second row should have
www in the first field, and your ip address in the second field. This makes
http://www.example.com show up. You can have more entries, for example, to your mail - or other subdomains.
In the following example both
http://example.com and
http://www.example.com will resolve to the same ip address - while
http://mail.example.com will resolve to another ip address.
[blank] 12.107.140.123 Default Edit Remove
www 12.107.140.123 Default Edit Remove
mail 12.107.141.456 Default Edit Remove