Downloaded apps not opening

[KOTG]

Hi there, I am a newbie to the forum with a new IPAD. I am experiencing problems with downloaded apps. For some reason the IPAD will simply not open any of the downloaded apps however all the standard apps work fine! I started deleting apps but this did not work. With some apps still installed I downloaded a new app and then hey presto all other apps opened normally. I have had this problem a number of times and although I have a work around it should not be happening. Does anyone have any suggestions? Many thanks.