How do I prevent"Crap"that pops on MY computer end screen at shut down?

I am an old retiree,novice to computers.I try to clear the computer screen one tab at a time when shutting down to learn what is running.The last CNN /Google/e-machine/weather channel/ etc. with message board pops up saying "error on this page may cause it to not display properly".I can not get rid of the message.I would like to prevent the (nuisance) board from showing automatically each and every time I attempt to shut down.Enough!|||You can try www.macory.com,it will let you Disable and Enable the ''Crap''