...you could try a different online scanner, such as F-Secure, and see if it helps. I think you may have to use Internet Explorer to use it though.
Use this. http://www.pandasecurity.com/usa/homeusers/solutions/activescan/default.htm?track=80383
It's panda antivirus' active scan page. It will scan and remove viruses from your computer threw a webpage without having to install. The only drawback is that you need to run it in internet explorer because it requires a plugin to run. Get the scan started right before you go to bed because it will take hours to complete.
I think both of them will probably work in much the same way, so you now have a choice, Baz.
I have to say, this sounds very strange. Can I suggest that you try downloading a little program called
EndItAll2, which will attempt to close / kill any running programs, while in normal Windows mode? Also, have you tried going to Start > Run > (type) MSCONFIG, click OK, then look at the Startup tab to see what starting with Windows? You might find something iffy in there, but seeing as you can't even open HJT in safe mode, that's probably a bit of a shot in the dark.
Just a thought, but in Outlook Express > Tools > Options > Security (tab), there's a tick box that says "Do not allow attachments to be saved or opened which could potentially be a virus". You haven't got that ticked, have you? If you have, untick it, and that
could be your answer.