Vista - Vista Screen Saver

After initial install all was OK. I then transferred files & settings from XP
machine. Since then the screen saver will not activate,system does not seem
to recognise the power saving settings, does not turn off monitor at all.

Any help would be appreciated, this was pre-installed so I have no CD to
re-run setup. Microsoft tells me the prod ID is invalid and the manufacturer
says its a windows problem.

I might just go back to XP but I dont trust this pre-installed stuff.