I cannot access some of my phones settings or apps I downloaded

Cant get online connection despite having turned on lication,wifi,& 3g. I believe I have a virus. Im not rooted &,have factory,reset,2×.Alot of my phone settings I'm unable to access bcuz they are grey or they flash back to previouse option. Only showing actual page or app for split second. Many unacessable strange files from xternal sd someone put into my phone downloaded & uploaded its contents & my contents if thats possible. Thanks from Computer illiterate