What is going on? For 3 days your servers have been unavailable!

What is going on? For 3 days your servers have been unavailable!

Since Wednesday, several times a day the invoice servers are unavailable. If I try to save or pull up anything it fails and I normally have to wait 15 or 20 minutes until they come back on line. This isn't a computer thing because it's like this on all my machines and it's not a network thing because all other sites work fine. Please advise.