Hard to describe so the picture describes it best, happens to him with any hud.
[img]http://images.akamai.steamusercontent.com/ugc/262720587546940349/1021B536C87F430C381D3925AFDE8E8F82F965D2/[/img]
verify the file integrity or his computer has been possesed by some form of dribbler magic
the game being confined to a tiny box in the top left makes me think it could be something to do with mat_viewportscale and mat_viewportupscale? Can your friend check to see if his values for those cvars are set to default ones?
a friend of mine also had this problem multiple times a while back, not really sure how he got rid of it though :/
https://i.gyazo.com/fc7275b6f49db7efe9eb61f271bd312d.jpg
https://i.gyazo.com/1a2b871a1437af8974ef74618e50c974.jpg
https://i.gyazo.com/2805266d69ace1ebd2ca649cc974ede4.jpg
https://i.gyazo.com/e490ade2847f2ddf5ac057bfbd4c80a9.jpg
https://i.gyazo.com/fc7275b6f49db7efe9eb61f271bd312d.jpg
https://i.gyazo.com/1a2b871a1437af8974ef74618e50c974.jpg
https://i.gyazo.com/2805266d69ace1ebd2ca649cc974ede4.jpg
https://i.gyazo.com/e490ade2847f2ddf5ac057bfbd4c80a9.jpg
i had similar issues when i was OCing my gpu so #9 might be the reason
mat_viewportscale and the mat_viewportupscale values were probably changed. try and set it to 1 or whatever the default was.