After closing the dishwasher door and turning it on, the water starts but
never has enough pressure to spin the sprinkler. It won't drain either, it
seems, so after every test, I have to mop it up.
PS I'm confused if I should post to this thread or to the long thread so
I'll try to keep an eye on both!

I think the other thread is dead.

You might want to check first the air gap and drain hoses from the air
gap to the garbage disposer.

Once you clean out the air gap and hoses, check for a broken belt used
to drive the pump.
Sometimes that belt just slips off the pump.
Replace it anyway because it might be stretched.

Then check your pump impellers. The wash impeller takes care of the
wash cycles, the drain impeller drains the water out. Check for broken
blades or shaft preventing the dishwasher from draining.

Before you go farther, check to see if the water shutoff valve
(located under the sink) is open or clogged. Remove the hose on the
dishwasher side to see if water gushes out. If not, clean or replace
the shutoff valve. If water is only dribbling out then put a pressure
gauge on the valve to see if you have at least 50psi. You can get
liquid pressure gauges from an automotive or plumbing store.

Always unclog the spray arms. Stick a paperclip or pipe cleaner into
each hole in the spray arm to ensure a smooth flow of water. These
holes are what spin the spray arm. If they are clogged, you get no
spinning action.

Next check your drain solonoid to see if it's stuck, preventing water
from draining. Smack that solonoid with a big magnet like those cow
pills if you have one handy. If not, mash it a few times with a
plastic mallet, taking care to only free up the solonoid if it's
stuck.

If the solonoid is ok, then see if the motor is stuck. This time, spin
the magnet around the outside of the motor to see if you can get the
vanes to move. Or stick wooden chopsticks inside the motor vents to
see if you can push the motor as sometimes the carbon brushes bend
against the copper commuter and the springs get caught.

Last, check the timer which runs the whole thing. And check the door
switch which turns it on.