To use more than one Skype account on the same computer at the same time you need to start a new instance of Skype.
From the Windows taskbar, click Start > Run (or press the Windows and R keys on your keyboard at the same time)
In the Run window, enter the following command (include the quotes) and press OK:
"C:\Program Files\Skype\Phone\Skype.exe" /secondary
If you get an error message, copy and paste the exact command from this page and try again.
Be aware that if you have changed the installation path for Skype then you will need to enter the correct path for the Skype.exe file.
If this solution fails, you can try another option:
Find the Skype executable file (Skype.exe) in: C:\Program Files\Skype\Phone\
Right click on it and select Send to > Desktop (create shortcut)
Locate the shortcut on the desktop, then right-click on it and select Properties
In the Target field, add: /secondary. The Target field should now be "C:\Program Files\Skype\Phone\Skype.exe" /secondary
Click OK. You can now start a new instance of Skype every time you double-click the new shortcut.
See Video Tutorial