DIAGNOSIS: The TV's internal storage is likely full from cached app data, or a specific app has corrupted. The Q60D doesn't have a ton of storage for the OS and apps.
FIX: Hold the power button on your remote until the TV turns off and back on (a full reboot). Then, go to Settings > Support > Device Care. Run 'Memory Booster' and then 'Manage Storage.' Delete any cached data for problematic apps. If that doesn't work, go to Settings > General > Smart Hub, and choose 'Reset Smart Hub.' This will log you out of apps and clear their data, but won't delete your accounts.
IF THAT DIDN'T WORK: A full software reinstall might be needed. Go to Settings > Support > Software Update > 'Update Now' to ensure you're current. Then, go to Settings > General > Reset. Enter your PIN (default 0000) and choose 'Reset All Settings.' This won't delete your installed apps but will clear all preferences and often fixes deep OS glitches.
HEADS UP: Don't use the 'Reset Entire TV' option unless you're desperate, as it will wipe all accounts and apps. Also, if you have a USB drive plugged in for recording, it can cause the hub to lag—try removing it.