Help!

Hello,
i need the dear forumers help. Gmod ran properly on my pc, but then i installed win7, and now when i try to launch garrys mod, it does nothign. my friend list says im in game for like 1-2 secs, but then it say im just online. plz help, i tried to reinstall it like 10 times, i googled, but nothing helped.
Thx for your help, have a nice day:
Wizilw