In the f1graphics.cfg there is a line called......
0 ; Full 32bit textures
Make sure that is says 1 instead off 0.
Happened to me severall times, did make my own liveries, looked oke, used another .cfg file where it stated 0 and hey presto i saw the original liveries from the game, changed from 0 to 1 and my own liveries where back.
And yes i always use the hi_ files off course.