You have trouble logging in Skype even though you could in the previous time. This article will help you to deal with this problem.
Step 1: On the desktop, open Start-> Run. Here, you enter msconfig into the text box and click OK.
Step 2: System Configuration window will appear, choose Boot. Then Boot options->Safe boot-> OK.
Step 3: There is a notice appears asking you whether you want to restart your computer or not. Choose Restart now. Remember that if there is no restart notice, you still need to do so for Safe Mode.
After restarting your computer, find Skype icon on your Start menu and right click on Quite to completely close Skype.
Step 4: Open Start-> Run, enter "%appdata%" and then OK.
Step 5: A roaming interface will appear, let’s find Skype folder and change its name to any other.
Step 6: Return to System Configuration-> Boot, unstick on Safe boot, then click OK. Finally, restart your computer and try to log in Skype again.