There are 3 main reasons no users would be able to log into Profile on an on-premise setup:
The Profile database server is off. Ask your IT to check the server is actually currently running. If not, they can start it back up.
There is a network or server issue preventing users from connecting to the database server. Your IT can run ping tests from users' PCs to the database server to establish if it can be reached.
The Profile engine is not running on the database server. To check this:
On the server open the program SQL Central.
The first window shows Plug-ins. Under the Name column, double click SQL Anywhere.
Two tabs appear: Servers and Services. Click Services.
A Profile7 service will then show and the status of if it is running or not. If it is not right click Profile7 and click Start. Users will then be able to log in.