Hm, the only thing left is a hardware error, a problem with some files or malware which could cause that.

Is there much dust in the computer? Does the CPU fan runs correctly? If the system is getting to hot it could provoke a memory reading error. If there is too much dust then please try to remove the dust before doing scan.

Where exactly does the scan freeze. It may be helpful to know that. There is a tool from Microsoft which can monitor the file activity:
http://www.microsoft.com/technet/sys...s/filemon.mspx

Just run Filemon before starting the Spybot-S&D scan. By the way, do you have added any download directories in Spybot-S&D? If yes, please try to remove them.

For checking if malware is the clue please attach the Spybot-S&D log file which Zenobia has requested.

Please continue to give us your feedback. It could help other users as well.