I've experienced a very strange problem on my PC at home recently. This runs Windows98 SE (with all the current MS updates), and I always have my personal firewall & AV scanner active whenever I access the net. About 2-3 weeks ago I installed RealOne player (the free version) and have used it with no problems, although I did instruct my firewall to block its attempts to access the net. Yesterday, some things stopped working properly - specifically double clicking on a Word document caused the PC to hang, as did opening Start/Settings/Control Panel. What I don't understand is that activating Word via a shortcut and opening the same document worked fine! I have made sure my AV scanner is up to date, done a manual scan, checked for trojans all of which came back clean. The symptoms were repeatable and persisted after a hard boot. Having drawn a blank there, I adopted standard procedure and uninstalled the last bit of software I had installed (RealOne) - I made sure all its Registry entries were removed as well. Having done that, everything works fine again.
Do I have some virus that my AV scanner doesn't know about (McAfee), is it something to do with RealOne (I know it does some odd things with file associations), or something else?

Any comments would be most welcome ....