This is a Vista Home Premium computer ..correct?
Could you tell us a bit more about the
system you are working with?
Do we understand you have more than one antivirus program installed ?
How does the computer connect to the Internet ?
From what you have already said it is quite possible you have a conflict with your protection programs that may have caused the computer to lock up; plus maybe too an infection has got in if you have multiple antivirus programs attempting to protect it