Inspiron 3501 Display and external display stuck

Sometime my laptop display and the external display get stuck with distorted screen this make the laptop completely unresponsive to any input. I could only turn off by pressing the power button. When I remove the hdmi cable, Laptop restarts sometimes. I'm not sure the fault is in the laptop or the external monitor.
Laptop: Inspiron 3501
Monitor: Asus TUF VG1A Series.