Hyperlinks “invisible” in HTML mode, but appear in PlainText mode

I'm used to creating emails in HTML format so I can insert "live" hyperlinks. Usually, when you Copy and Paste a hyperlink from a web page into an Outlook email, the link is shown in blue and is underlined. Mine no longer does that.

I know this sounds weird but recently, when I paste link in HTML format, it doesn't show up on the page! Nor does it show  I do Ctrl-V to paste, the cursor remains in the same location, and the link is "invisible". I say "invisible" because if I go to the Options tab, and choose Plain format instead of HTML format, the link appears in blue, but all the formatting is gone.

If I send someone this "invisible" link, their email looks blank. But, if you "View Source", the link is clearly shown!

I've made sure I have the latest updates for Outlook and I've made sure that all the application Preferences and Settings are correct, but I still have this problem. Has this ever happened to anyone else?

I would like to try re-installing Outlook, but I don't have a disk. What can I do?

Thanks

Chey