Why won't Picasa email my photos?

I'm smart enough to take good pictures but can't make Picasa work. I want to email pix. Windows XP. I follow instructions but can get only as far as putting pix in tray, hitting email icon, and getting a blank full page presumably from my default email Yahoo that says 'compose'...no cursor, no places for addressee, absolutely blank; no indication of where trayed pix are, for attachment...nothing. This is not an excess photo-load problem.