Notice: If you have our Fully Managed Support You don't even need to follow these steps. An administrator will go in and fix it without needing to contact us. If there is nothing wrong with the VPS though you can always open a ticket and you'll have a solution within usually an hour.
There are 4 main reasons why you wouldn't be able to get into your server:
Your software isn't running
By far the most common is the software you're trying to connect to has simply stopped working. Nothing is wrong with the VPS but rather the software you installed. Make sure that it is running.
There is some Network or Hardware Issue
First check the Network Status page to see if there are any known issues that are happening. System Admins will usually add some entry there once they can figure out the cause. If there are no entries there then go to a site that can ping your server from different locations like https://asm.ca.com/en/ping.php and put in your ip/hostname. If any of them are able to ping your server then there is a good chance that your server is blocking your connection.
You were blocked by something on your server
If you have something on your server that blocks users for too many failed login attempts or other similar actions this might be the case. To get around it connect from a different location such as work, a VPN, or the SSH feature of the control panel.
Your server was hacked and the IP Null routed.
When you have a VPS it doesn't matter who you purchase it from you are responsible for the security of your vps/server. If you installed some malicious or outdated program, or someone was able to break a weak password then an automatic system in place would have Null Routed your IP meaning that it is "turned off" until the problem can be confirmed as solved. This is done to protect the safety of our network and other users. It also stops these attackers from spreading their trash elsewhere. To get this resolved you would need to POLITELY open a ticket in support asking if your IP was null routed. We will be able to check and if it was then your only option usually is to reinstall your VPS and wait the time it takes for us to verify that it is solved and get it activated it again. This process is quite serious; so it is best to avoid it altogether by making sure your do some basic things to stop hackers. You can read about them here: How do I stop hackers from getting into my server?