Speedometer quit working

:( : 99 taurus stn wgn
mileage too high 174000
just until last week no problen and of course as soon as paid off warranty no good
my speedometer started jumping while on the highway and now is not moving at all
have no extra money for live mechanic so web hopefully will help
i have some mechanical knowledge but really is limited to the old straight 6 room to climb into engine
please help
i try to use my tach but for a school zone I don't like to take the chance and try to avoid at all costs
other problem just since quit my check engine light came on
could that be the only reason or is there another thing that I should look for
thank you
kathy