If you can get to a point where you’re asked to enter your sign-in details, continue to step 4.
If you can’t get to the sign-in screen, there might be something wrong with the way Skype is installed. Try uninstalling and reinstalling Skype.
If you can’t get to the sign-in screen because Skype is already signed in with a different account, click Skype > Sign out in the menu bar (File > Sign out on a Mac) and then sign in with the account you want to use.
If you get an error saying Skype is already signed in on this computer, restart your computer (making sure there are no pending operating system updates first). This usually solves the issue. If it doesn’t, try uninstalling and reinstalling Skype. If you still get the error, contact Skype customer service.