Hi Daddycat.
Rest assured, that even if your OS
is corrupt, there is a fix for this - although it entails a format + reload of Windows. Unfortunately, it's hard for me to service your system through CC forums.
Why is it your Flash cannot be updated? If you're willing, I'd be able to connect to your PC remotely using a certain program to try to correct the Flash Player problem. But as for your OS; I'm afraid you will need to re-install Windows XP, unless you're using a PC with a good recovery partition, in which case you can use the built-in recovery to restore the computer to it's factory condition.
Feel free to PM me if you like!