ActiveCollab works from a single address, https://projects.mycompany.com for example. When you try to access it using a different address, it will broke and get stuck with spinning wheel.
Installer will set this address for you when you install ActiveCollab. In some cases, customers like you will use localhost to install the system. When installed like that, ActiveCollab works fine, but it is accessible only from that one computer.
To correct this, you should change the address that ActiveCollab works on. Use address that's accessible to everyone who needs to use the system. Switch from localhost to computer's IP address to make it available to people in your office. If that address is available from public internet, people will be able to access when they are out of the office.