on a notebook Compaq with Vista Home Sp2, certificate (v11 pro) is accepted but after reboot it's lost; i checked "Registration Certificate installation problems" thread on this forum and all seems fine: permissions are ok, no antivirus running, certificate is valid and genuine.
Copy and paste make it work again but have to do on every boot. What else could I do?
And then, how can I know in which computer (or in how many computers) my license is used?
Make sure compatibility mode isn't on (as per Abr's link; plus anything else in there you haven't tried, although it sounds like you've checked some of that already).
Also, check that the C:\ drive is formatted as NTFS, on the off chance it isn't. (Right-click the drive and open Properties, then on the General tab check where it says File system: NTFS, or similar.)