"My Computers" page lists host computer as "Unavailable" or clicking 'Connect' never establishes a connection. There are three issues that may cause a host computer to go unavailable: 

• The host computer is powered off or in sleep mode 
• The GoToMyPC host software is not running 
• The host computer is not connected to the Internet

Troubleshooting steps:

1. Confirm host computer is turned on and not in sleep mode
2. Confirm GoToMyPC is running (look for system tray icon) on host computer
3. Ensure host computer can access the Internet (try navigating to www.google.com or another webpage)
4. Confirm your security software allows GoToMyPC to access the Internet

Information on Sleep mode : http://windows.microsoft.com/en-us/windows7/Sleep-and-hibernation-frequently-asked-questions 
If MyPC icon is not in the menu bar on Mac OS X: Reboot the Mac 
For assistance allowing GoToMyPC in security software, please contact security software provider.