As I am relatively new to the field of gardening and my knowledge in
this area is very limited, I tried to rely on fertilize/weed control
packages from Scott's. For the last 3 years, I used their 4 steps
program and apply each of their steps according to the instructions on
the label. I also spent a lot of time manually removing some of the
weeds, but that doesn't seems to help as the very next day my lawn is
yellow again from dandelions I have missed.

I don't see many dandelions in your pictures, but you've got a fine
stand of lily of the valley, some thistles, ground ivy, some
violets, and some exceedingly dry grass that's been chopped by a
dull blade on the mower. Of those, I'd transplant the lily of the valley
to an area where it can be contained, keep the violets and go after the
rest of it.

What's the soil pH, what was your last soil analysis and when, and
when and how are you mowing? Have you ever lifted some sod to check
on root structure? If you water, how deeply and how often? Where are you?

Plants require not just fertilizer, but also water, oxygen to the roots,
and care to look really good. You're substituting sacks of magic potions
for basic understanding of plant biology, and it's not working so well.

In the meantime, lift some sod in the thick areas and in the thinner ones
and really look at the structure of the roots and of the soil in those
areas. Submit a sample for soil analysis. Get the lawnmower to the shop
and have the blade sharpened (those ragged browning edges are a good clue
that the blade is dull.) Learn the correct mowing height and procedure
for the species in your lawn. Consider overseeding in areas where the soil
is bare, but be sure to scratch the seed in well and tamp it down and keep
moist until it's well established.

An excellent beginner's book, imo: Rodale's Chemical-Free Yard and Garden --
you should be able to pick up a used copy on the net for $5. Pay special
attention to the chapters on soil and water, as well as those on lawns.

See also:
http://abe.www.ecn.purdue.edu/~epado...homeowners.htm
http://www.ncagr.com/agronomi/samhome.htm
http://www.ncagr.com/agronomi/ustr.htm
http://www.ext.vt.edu/pubs/compost/4...ingsample.html
http://muextension.missouri.edu/expl...ort/g06720.htm
http://clean-water.uwex.edu/pubs/yardcare/lawnwat.pdf
http://www.extension.umn.edu/info-u/plants/BG529.html
http://www.ext.vt.edu/pubs/turf/430-002/430-002.html
http://www.urbanext.uiuc.edu/lawntalk/lawntalk09.html
http://www.gardening.cornell.edu/law...re/mowing.html
http://abe.www.ecn.purdue.edu/~epado...p/cutting4.htm

Kay