microcenter tech

I have know Idea what is wrong it is hard for me to explain but I have sent my computer to microcenter twice, They have had it all week and when I get it back it is even worse than before.
The colors are horrible on my computer, it looks as if the settings are wrong, I go and change them and they are fine for about 5 mins. then it goes back. I get it back from micro center and they have NIVIADIA? Now I can not even change the icons to large, they remain small And I can not read what I am doing. The computer will not let me make a back-up of my programs- files, and it freezes on the internet and sometimes off. This computer is so screwed up. Can anyone help?