Okay well, Check your color setting (i.e. check if its 16 bit, 32 bit or 64) and make sure combat arms runs on that too. Do the same with the resolution. Set Low quality setting on combat arms. Also, check if your ram is enough to process combat arms AND windows 7. Windows 7 uses up a lot of it ( i personally think vistas hella better).
If none of this works, send a ticket to nexon about it.
1 more thing, check your connection, maybe its not good enough to run an active fps online game.