CF Froze, Lagg, Lost Server etc.....

HY.
Its only at my PC with Win7 OS, XP runs.

Unexpected the Screen Frozes, cant move Mouse or use Keyboard.
Sometimes after a while there is a crazy Buzzer Sound in Speakers.
Than after a long long while, screen shows: Lost connection to Server....
Sometimes i was out of game, or out of CF.
There is not Timemode. Sometimes i can play a long time, sometimes it happens every 15 seconds...
.NET 4, Direct X 11, Flashplayer 11, Win 7 Dayli updated. (Win 7 Professional 32 Bit)

Maybe the McAffee is it? But if, why sometimes nothing happens?
I got 2 identic PC´s, one with Xp, one with 7 which makes CF Problems, normal Working on this PC runs.

So what can it be?

Greetings