Thanks ClubMan. I had uninstalled and reinstalled Adobe several times yesterday but still no video even though the player appeared OK. As I mentioned, all the previous System Restore points disappeared during the process of transferring My Docs files to the spare hard drive. I didn't meddle with the Registry either and didn't knowingly delete anything other than some files in My Docs and some emails. The reason I wondered if the Registry was mucked up was because I read that was a possibility on the Adobe site.
The good news is that it's working again! I had another go just now at uninstalling and reinstalling the Adobe Flash Player and, amazingly, it solved the problem - it's working. Thanks a lot for the advice. Now I can watch my new addiction - the U.S. nomination process.