Runaway exception on 0.9.3 Bitcoin client startup 64 bit Windows 7
I'm not an expert on Windows, but I suspect your problem is caused by your anti-virus program.  As widely reported, some griefers have placed virus signatures in the Bitcoin block chain.

These virus signatures can't actually harm your computer---the block chain is non-executable---but virus programs detect them and quarantine the files anyway.  You may want to poke around your anti-virus program's settings and see if there's a way to exclude bitcoin-qt and its data directory from your scans.

Although it won't help you now, it might ease your mind to know that the Bitcoin Core developers are working on this issue.  If I understand correctly, their plan is to optionally allow each Bitcoin Core user to store the block chain with a slightly different encoding[1] so that virus signatures in the block chain are uniquely obfuscated on each computer.

[1] For compsci geeks: they plan to allow XORing the block chain it by a bitstream unique to each instance.