個Youtube 芒好大

YouTube screen sizes range from small player, large player and full screen. Assuming you are staying on full screen.

1. First up, tab the ESC key at top left corner of your keyboard to quit Full screen. It it works, you can further reduce the screen size by clicking Small screen button at the bottom right corner of the YouTube screen.

2. Otherwise, outside Full screen, you can press and hold the Ctrl key with your left hand then roll the mouse wheel back and forth to find the exact size you need.

Hope this helps. There is also an outside chance that your screen resolution has been changed inadvertently. If problem persists, launch your display card interface and check the resolution settings for correction.

2014-04-12 15:41:52 補充：
If it fails, you'll have to be more descriptive on your PC system. Post what you'd done before this happened plus a brief summary of your computer hardware and your O/S.

Every little bit helps. Even the doctor needs your medical history to home into a correct diagnosis.