My mail window in yahoo beta only shows my mail titles. I have to highlite then double click right.?

This opens another window that allows me to open the mail i mean to say. Before all i did was go to my mail highlite what i wanted to see and i was able to read the contents or open attatchments on the lower half of the screen, which now has mysteriously vanished, or morphed into a single screen instead of the split view where i highlited then viewd on the lower half