Thank you all for the references to previous posts on this issue. I had no idea it was such a widespread issue. I have dragged and dropped a couple of PTE 5 AV's to a USB pendrive and then copied and pasted the AV's to the desktop of the problem Vista laptop. The smaller AV ( 7mb) closes OK but the second AV ( 25mb) fails to close at the end. When I press Ctrl,Alt, Delete I get a message "program not responding". There is a tab that says "view problem details" and when I click that I get a description : "A problem caused this program to stop interacting with windows". Then there is a list of "Problem Signatures" : Problem Event name - "AppHang B1". Hang Signature - "fb8f". Hang Type - "515". there follows more "additional hang signatures". Only a technician would understand the above but as a layman it is simply that Vista does not work with PTE. There was a suggestion that the Laptop should be taken back to the retailer - in my case PC World - and I may have to do that. But I will try your last suggestion,Igor, before I resort to such drastic action. Tom