Half life 2 problem

so i´ve been playin HL2 for some time and there was a problem with the HUD that wouldt go away unless i changed the water reflections and then change it back again, so i did that but by accident i changed the screen mode to panoramic (4:9 or 4:16 i think) and now i cant see the game, all that appears is like some white stains and then they turn to black then to white again, etc... i can hear sound but i cant see what im doing.
anyone knows how to fix this? i already uninstalled it and re-installed it 2 times, without seeing what im doing i cant change the screen mode again...