How new is your system? which games are you able to run without problems? Is it a illegal version?(probably not, because you're playing multiplayer) If it is, maybe downloading an other version might work.

But if no one on the forum was able to fix the problem, you're probably need to wait till Blizzard releases a new patch(altough i would doubt this, as it as getting a rather 'old' game) or wait for an upgrade for your computer.

What video card do you got?

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