I have this problem too. Two days ago when I started Y!M in the morning all the text was gone. I can't select the text, there is nothing. Even in the Message Archive is the same, I can select the days but there is no text. And this is hapening at my work and at home, the same thing on different computers, different Windows' (WinXP & WinXP x64). And as I see also Internet Explorer has problems, I can't open some pages at all (with Opera no problem).
I read somewhere that Y!M depends on IE's Scripting settings, I tried different settings but without results.
I scanned the PC with anti-virus, anti-troian, anti-anything but found nothing. I have no idea what's going on.