The computer is a high-end laptop just out of warranty (of course), running 32-bit Vista Ultimate, SP2. I cannot manually create a restore point and the last one automatically created was over 6 months ago. The specific error message is: "The creation of a shadow copy has timed out. Try again this operation."
I read the previous post and answer for a similar question (7-8 January 2010) and tried its recommendations 1 and 3, without any success. I did not try number 2 because it was not clear to me. My computer experience has included replacing memory, drives, video cards, etc., and a lot of software configuration, but I'm not comfortable changing sensitive PC settings unless the procedure is crystal clear.