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Try going to MS and updating to SP2 again, but close everything else out. You may have to put your firewall (if you are using a third-party FW) into Learning Mode; Windows FW is fine.
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Please try upgrading from the obsolete version of Avast you have to the current version of 6.0.1125.
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Have you done recent scans to make sure you are clean (no infections/malware)?
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What other security software do you currently have or did you have in the past on this machine including: