My PC Always Hangs Whenever I'll watch an online video or even start video chat

My PC Always Hangs Whenever I'll watch an online video or even start video chat

My PC has recently started hanging completely whenever I start online video or video chat. Nothing works, even tried Ctrl+Alt+Del and mouse does not respond, leaving me only one option of hard reboot. I changed my monitor recently. Don't know whether it is the cause of the problem.