If it is windows 8, you should be able to hit control key, alt key and delete key at the same time, this will bring up a menu which the last choice is Task Manager, open that and then you should be able click on the program that is generating that error window and shut it down. Once done, you need to run a scan on the computer to see if you have bug, also make sure Windows defender is on and is up to date. By the way, don't call that number, if you do, you will be set up for daily robo calls for at least a year if not more!