Please Check your system Settings.
Open Power Settings under Control Panel -> All Controll Panel Items -> Power Options.
Click "Change plan settings".
You'll find "Change advaced power settings".
Search for "Swichtable Dynamic Graphics" in the "Power Options" dialog and change the "Global Settings", "On battery" and "Plugged in" to "Maximize performance"
Now both, HeavyLoad and other programs which have the same problem shoud work again.
Also make sure you have the latest drivers installed for your graphics cards.