It may be that you need to delete some apps (depending on how many you have).
Before you do, try the following:
ATTENTION: If you still cant load YouTube/YouTube (or other apps):
1) Check for updates: Settings/System/System update/Check now
2) Restore the default theme: Settings/Theme/Restore default theme
3) Use a simple screensaver: Settings/Theme/Screensavers/Roku Digital Clock/Set as screensaver
4) Load YT/YTTV/apps
** EVEN IF YOU ALREADY PERFORMED THESE STEPS, DO THEM AGAIN **