The only suggestion I can think of right now is to reboot again until it starts up normally.
Hold down the on/off button until the screen goes blank, it should then restart
My tab 2 has done that before, as has my mums tab 3.
It may be going slow because of a secondary app that downloads with a main app (games etc)
Every now and then I go through my apps list and un install anything that looks dodgy or I don't know what it does <_<
Usually it's advertising video caches and the like ^_^
Hope that helps