Had a call to look at someone's PC - the BBC iPlayer wouldn't work, neither would internet banking, and McAfee Security Centre was blank when it loaded up.

I ran IE7 as administrator (Vista Home Basic) and it worked fine - tried this with McAfee as well and that also worked, so i thought it may have been a permissions issue.
Turned down IE7 security settings, but still nothing, so started Googling it...

Found this link on the McAfee site:

http://service.mcafee.com/FAQDocument.aspx?id=107121&lc=1033

And tried this part of it:

1. Click Start and select Search.
2. In the Search box, type CMD and click OK.
3. In the Search results window, right-click CMD and select Run as Administrator.
4. In the command prompt, type REGSVR32 JSCRIPT.DLL and press ENTER.
5. After the confirmation message is displayed, type REGSVR32 VBSCRIPT.DLL and press ENTER.

It then says to uninstall and reinstall McAfee, but i tried it straight away and it worked for everything without any reinstalling needed.
Rebooted just to make sure it still worked and all ok.

Not sure what caused it - whether a Java install got corrupted or something, but all sorted now.