Please note that when your Mac goes into sleep-mode it loses its connection to the internet and as a result, the hopTo App on your iPad will show your Mac as offline. You can modify your Macs sleep settings in the following manner:
Click the Apple Logo in the menu bar (upper left hand corner on most Desktops):
Apple Logo->System Preferences->Energy Saver
You will see the following when choosing the Power Adapter Tab:
Set the slider for Computer Sleep to the appropriate settings for you. Setting the slider to Never, will insure that your Mac is always available to access the internet.