OK. This gets more interesting by the minute. The correct download in this link (
http://support.microsoft.com/kb/947821) appears to have resolved the problem but I thought I would run
just to double check but got the errors (on the attached file) as well as the msg in the command prompt: "Windows Resource protection found corrupt files but was unable to fix some of them". I don't know if this is something serious or that can be ignored.
I had also previously had to go to a restore point as well as running chkdsk.
I don't know if this is all pointing to a complete reinstall because if it is I should start backing up my files now.