you should post a screenshot so we can see whats occuring. given the information though it sounds like you activated one of the alternate view options. this is done by either by changing options in the show menu (i think its thats menu i odnt have unreal open atm) or by pressing certain F number keys. to fix this you either need to find the options and set to lit mode or press the f num keys until you find a view you like (i think f5 is lit mode).