Cortana is great if your going to constantly use her help but in a situation like your I would advise you to shut Cortana off to avoid this from happening unless your going to use her services
It would a great choice if you don't have much things to download due to it's limited storage capacity but otherwise I great phone I owned before I decided to upgrade
First off you must run your anti virus to check to see if your pc has malware if that turns out ok you may want to check to see how much memory you have left having too much stuff running slows down a pc abitlty to perform well