Please tell us more about your setup. What is your computer? What is the second monitor connected with?
If you unplug your second monitor and do a restart, the issue will be corrected usually. If you cannot see your screen, then I suggest a hard shutoff as last measure. Wait till there is absolutely no HDD activity, then hold your power button for 5 seconds or more, until the PC shuts down. Unplug any monitor that is extra, and restart the PC>