First you need to determine what is down. Your server, your connection to it or your Geo software. If you can get to your site or more specifically you can see other elements hosted on your domain but can't get to anything in your Geo software installation we're the ones to consult. But if you can't get to anything hosted on your site this can be one of a few things:
You can check any connection issue by using tools that trace the ip route between you and any destination on the Internet. The command is "tracert" on Windows while the same on a Mac is "traceroute". You run both in the terminal mode or command line in your computer. You should search the Internet for more on either if you need to know more about them or details using them.
If you can't get to your Geo software what do you see when you go there? Do you see a "site maintenance" message on your client side and see your admin tool? Do you not see the software at all on the client side or in the admin tool? If any of those check that something hasn't changed in your server environment. Many times hosts upgrade software on the server like the operating system, PHP, MySQL or other software running on the server. Your host could have upgraded the server hardware or simply moved your installation to another server altogether. Basically all of the above fall into the "server environment has changed" category and first is to verify that the server environment still meets the needs of the software as explained in the minimum requirements of software page of this wiki. Special configurations may have been needed at the installation of your Geo software to make sure the server environment met the minimum needs of the software and if things are changed in the server environment you may need to reapply those special configurations to your hosting environment. If your domain was moved from server to server this can constitute a change in the environment also. Hosts try to make these changes as painless as possible so as not to disturb your domain but invariably at times they do have an impact. Moving from server to server can change the installation path of your software and this will affect the license of your Geo installation and throw up the "site under maintenance" message on your client side and show you the actual license error if you log into your admin tool. If you detect an installation path change send us any license errors you see and we can quickly update your license. For all other issues Geo contact Geo support and we can take a look.
The "server is down" is the least likely of those to happen because linux servers which is what the vast majority of our clients use can be up entirely from the time they are turned on to the time they are decommissioned though there usually is an upgrade or two here and there. It is very easy for hosts to make the 99.99% uptime guarantee. But note that the server being "up" AND still able to support your Geo software can be very different things. The thing you are not told by hosts is that they do not make the same guarantee for their Internet connection. So while that hosting tech you are talking to at your host says "they see your server just fine" every time you talk to them they are most likely seeing that server on a close local network that never goes down either. Also "seeing your server" doesn't mean that everything on it is working properly either.
So have a checklist the next time you think your "server is down" and verify what is "down". That way you know who to go to first for a specific issue.