Personally, I wouldn't risk it - the files could conflict thus decreasing the performance of both Antiviruses. Stick to one, and make sure it's a good one too.
Thanks everybody. I have installed both Kaspersky antivirus (KAV) and Antivir personal. Nothing was responding in the beginning. Somehow opened the task manager and shut down the antivir virus guard process. And it was normal again. I have scanned my pc using both the two antivirus (not at same time ofcourse). I think the only problem is with the constant virus-monitor thing, they fight with one another.
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A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.