I have a late 2015 iMac 21.5" running OS 10.13.6. We use this machine for surfing, daily living functions, photo and music storage. We have real issues with this machine, such as: when trying to open a link, the linked window will show up briefly, then turn to a white screen with a spinny thing - sometimes we get the white screen with the little blue box with the question mark. Is this because of a setting issue, or because the OS is so old? I appreciate any assistance. Thanks...