Can't Login to my Server via SSH, and the password is correct

I'm using Linode, and I've asked around on the IRC channels, but no one seems to know. I've logged into my server via LISH (reference), and I used the correct password, and everything went fine. However, I need to login via SSH/FTP, and I can't. It keeps on giving me "permission denied". I know the password is correct because I reset it via LISH, and I know I've got the login method right because I've logged into my server before using the exact same commands. I sure hope this doesn't turn out to be some noob issue, or I'm going to be quite frustrated.

You need to run ssh (the client, and possibly the server) with more verbosity to understand why authentication is failing. For the client, run

ssh -vvv username@host 

On the server end, check the logs. /var/log/auth.log will give you a pretty good idea about what happens when you try to login, look for messages that contain sshd. There are a variety of reasons why authentication could be failing, ranging from simple (you aren't using the right username) to more complicated (sshd is configured to use the wrong authentication system).

in my case our IT department had setup PAM stuff with rules that broke my login. followed @pestilence 's reply to see error, ended up commenting out AllowGroups in /etc/ssh/sshd_config, which was setup to some IT stuff:

UsePAM yes
#AllowGroups <some IT groups>