garrys mod wont work HELP

OK so i got steam a week ago and i downloaded tf2 i played for a while. then today i bought and installed Garry mod but it wouldn’t work (every time i loaded it up it went to a black screen froze my comp and i had to turn off my computer) then i tried installing source sdk because some places said that would fix it. but it didn’t work so i uninstalled everything then i installed half life 2 and bought it because some places said i needed to. then i installed Garry mod then boom same thing black screen. and it wont work any one know a fix ?

Post in the HELP/SUPPORT section if you need HELP. This is not the place.