Ok I've fixed this now. However, it was a little more long winded than I imagined!
Firstly, I deleted my Temp Internet Files and reset the IE settings.
Then I went to Control Panel - Folder Options - File Types and waited for it to load.
I then scrolled down and selected HTML files, then Advanced.
Although Open, Edit etc. options were there, there was no View! So I added a View command and selected NOTEPAD.EXE as my chosen prog from C:\WINDOWS folder.
I then OKed it and tried "View Source" too see if it worked. Nothing happened. So I then downloaded Tweak UI and went to the "View Source" settings. Notepad was listed, but it obviously wasn't working, so I went to "Change Program". It said there that it was pointing to the C:\WINDOWS\system32 folder for Notepad.exe, in spite of me not selecting the system32 folder earlier! So I changed this to C:\WINDOWS\NOTEPAD.EXE, started up IE again, and everything worked fine!
Thanks for your help bvw in bristol.
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