I was in the same boat this spring, since my house was a repo. I
manually removed all the dandilieons. I literally went after them
every day for about two weeks. Haven't seen one since. The weed
killer I used after that got any remaining dandilieons and cloves. To
get rid of the crabgrass I used Roundup. After it was dead I pulled
it all out, even the root system. I did a lot of digging! Think of
Crabgrass as the Viet Cong with an elaborate underground maze and
you'll get the idea of what your up against. If you miss a spot,
crabgrass grows back from a piece of root, so you have to kill it
first! The other weedy grasses (goose grass
http://www.blitzworld.com/lawn/image...%20SVG288F.JPG)
is also something I am still trying to get rid of. Nothing works
particularly good on it except Roundup. In fact, I'm reasonably sure
that I have some of all of the weedy grasses shown on this webpage:
http://www.blitzworld.com/lawn/weed%20grass.htm

They are just about the hardest things to get rid of because they are
the same color as your lawn and so far don't respond to chemicals that
attack just them real well.

Areas that I killed off, even several times over during the summer
with roundup (as many as 3X in places) I've replanted and in some
places it's regrown just fine, and others not. The places where it
didn't I'll probably try again next spring. I know your not supposed
to turn around and plant grass a few days after Round up, but if the
weeds can grow right back, I figure that grass can too.

Also, I pull all killed weeds, and till the soil before I replant. I
suspect this is why it is able to grow back in some places pretty good
as I've not been drenching the lawn with Roundup, rahter using it
sparingly.

Deapite years of neglect and nobody living in the house, parts of my
yard actually look pretty good now. It took a lot of work though.