Here are some basic trouble-shooting steps that you can try if you are experiencing problems in logging in or running Skype. You may have already tried some or most of these procedures, just try whichever are still applicable. If possible try them in the order they were listed as the first ones would most likely fix the issues;
1. Be sure that Compatibility Mode is not enabled (right-click on Skype shortcut icon/launcher and select Properties >> Compatibility) - for Windows 7 users only.
2. Enter %appdata%\skype in the Run command (click OK), then look for and delete file named shared.xml.
3. Update your display, audio, webcam, microphone drivers or software. You can also visit the corresponding manufacturer's site to check if there is a new driver for your device.
4. Try to temporarily disable your anti-virus or firewall software, just to check if they are affecting Skype processes in any way. Just don't browse any webpage or use any application that uses internet while your anti-virus or firewall is turned-off. Immediately reactivate them after checking/testing.
5. Do a complete uninstall, then reinstall Skype. here is how to completely uninstall Skype (just back-up all important files and information that you feel is important to you)
support.skype.com/en/faq/FA10634/How-can-I-completely-uninstall-and-then-reinstall-Skype
6. Run basic computer maintenance such disk defrag, registry cleaning, disk error checking, etc - and also run a full virus scan (just to make sure that your computer is free from any virus/malware that are possibly affecting Skype performance).
If all else fails, you can consider the suggestions below;
7. Restore your computer to a point where Skype was still working.
8. Try to disable or remove add-ons or programs installed prior to the existence of the problem.
