There are a limited number of computers you can be signed into with SketchUp. If you are unable to sign into SketchUp you will need to manage activations and deauthorize computers.
Click on Manage Activations
Click on My Products
Click on Installed Applications
Clicking View Included Applications shows all applications included in your current subscription. Look for the SketchUp Pro tile and click Manage Devices. The Confirm Deauthorization window will appear.
Clicking Deauthorize All logs you out of SketchUp on each of your devices and you’ll get a confirmation message letting you know your changes have been completed.
Once you’ve deauthorized your devices, you must Sign out of SketchUp (not just the web page but the software). Login again on each device you use SketchUp applications on. If you had SketchUp open on a device before you deauthorized all devices, you must close it and relaunch the application.
If you do not sign out, you will continue to get a message stating that you have installed SketchUp on too many machines.