dvi no output

[Ed Sykes]

Hi,

I'm writing a thesis... using LyX 1.5.5.2 on Windows XP, using MikTeX 2.7
for some reason the output is all blank... it has the right number of 
pages but all output in the dvi viewer (Yap) is blank.
It was working fine a minute ago...
i was just editing stuff in LyX... and now there is no output....
the last time i corrected this I re-installed MiKTeK but this seems to be 
a bit extreme.

Any suggestions are deeply appreciated !!

Thanks,
Ed Sykes