There are several possible reasons why Skype on desktop might not be starting.
The most common cause is that your system does not meet the minimum requirements of the latest version of Skype. For more information, check the Skype system requirements.
For Mac, you should also make sure that your version of Skype is up to date by using Software Update and installing the latest version of QuickTime.
Another common issue is with the default text-to-speech setting on Mac OS X. To change the default text-to-speech setting:
- In the menu bar, select the Apple menu, then select System Preferences.
- In the System Preferences window, select Accessibility.
- Select Spoken Content.
- In the System Voice drop-down, select anything other than the current selection.
- Try to start Skype again.