Infected?

I spent most of last night trying to figure out if my computer had the DNS Changer virus or the Flashback Trojan virus ... my machine was going slow and I couldn't access some of my blog functions, plus the icon for my blog had changed from the purple square to an orange O, perhaps indicative of the Microsoft Outlook Express page that kept appearing and asking me for my password (I don't use Microsoft). Things were complicated because I have an old OS and most of the detectors were for later operating systems. Finally downloaded an old version of a virus detector which couldn't find a virus on my machine, and now things seem to have just self-healed - the purple icon is back :)