I've run the sfc / scannow command. took a long time to go through all the files, asking me several times to 'retry' the Windows CD, but always proceeding OK when I clicked 'retry'.
Finished eventually, and closed without any message as you said.
Unfortunately the problem is persisting - still many blank pages, no videos, blank 'system restore' window, 'script error' messages on 'User Accounts' page and whenever I try to print/search from a web page - everything as before.
Lots is still working, normal web-browsing, e-mail, other programmes etc.
Thanks for your continued interest, but where can I go from here?