Are you sure it is a wed5840swd as I can only find info for a wed5840sw0.
In any case a SW0 should be close to your unit. The below info is for a SW0.

Here are your parts
Parts for Whirlpool WED5840SW0 Dryer - AppliancePartsPros.com

See the attachment for the tech sheet

Does the unit make any noise when you try to start it?

[COLOR="Blue"]Can the dryness control board keep it from starting?[/COLOR]
No unless it does something very, very weird that I am unaware of.
The dryness control just controls the timer motor.
[COLOR="Blue"]
It is getting warm also. Seems like motor but not sure[/COLOR]
What is getting warm?
If the heating coil is coming on then it could be the motor.
As you can see in the wiring diagram the motor has two centrifugal switches. They close/activate when the motor gets close to operating speed.
One of them switches in the heater circuit, this ensures that the heater does not come on until there is air flow. So if you get heat without the motor turning there may be problem with these switches.
The other switch connects in the motor's start winding when at rest. So if it is in the activated position there is no start winding and the motor will not start.

One way to check for this is to push start the motor. This may require two people. Set the unit to mid scale of a heating cycle.
Then open the door and hold the door switch closed.
Then push the push to start switch.
Rotate the drum manually in the correct direction.
Be careful in case the unit starts up, you don't want to get hit by the drum vanes.
If the motor starts up then the centrifugal switches are the most likely cause.
Note: If the motor does not start up this does not eliminate it as being the cause.
Also if it does start do not let it run too long as you do not have the proper air flow when the door is open and that can blow thermal fuses etc.

Check that the motor is not clogged solid with lint (holding the switches closed).

where are centrifugal switches. Can they be checked or are they in the motor?

[COLOR="Blue"]I had it running while troubleshooting when I checked for 240 at terminal block with meter. All of a sudden it came on. Worked for a while then won't run now.[/COLOR]
This is strange. I would check for a loose wire. Sounds like you have a bad Neutral.
Also did you check both sides of the line for 120 volts. The motor runs off of L1 to Neutral.

[COLOR="Blue"]Seems like motor but not sure. Continuity from terminal red wire to motor. Winding at motor check 0.5 ohm diagram says between 2.4 and 3.6ohm?[/COLOR]
I am not sure what you are reading here as the motor is not connected to red.
FYI: The diagram shows the two motor windings. Each winding is 2.4 to 3.6 ohms but since they are wired in parallel the expected reading from 4M to 5M at the motor would be 1.2 to 1.8 ohms.

[COLOR="Blue"]where are centrifugal switches. Can they be checked or are they in the motor?[/COLOR]
They are built into the motor, take a look at it in the parts, you will see their connections. They can be checked but only when at rest.

[COLOR="Blue"]The only noise you hear when you try to start is the start sw activating, but you have to turn timer around & re-press start sw, to re-hear the sound, like sw is latch after pressing. Its a 3 terminal start sw, got continuity across 2 when sw pressed, is this proper way to test start sw?[/COLOR]
I have a pet peeve about this. I do not know why they call it a switch when in reality it is a relay.
Yes 2 wires should go to 0 ohms when you press the switch.
You may have been using too low of a meter scale so the meter coil read infinite ohms.
When you press the switch the circuit is completed for the coil and that hold the switch/relay contacts closed until the BK/BU timer contacts open or the door switch opens.

If your power checks out OK perhaps try the following.
Unplug the unit and attach one meter lead to the L1 connector at the line cord plug and leave it there.
Set the unit to timed dry mid cycle. Meter set on most sensitive scale.
Now work your way back through the circuit
BK on timer should be 0 ohms.
BU on timer should be 0 ohms.
One connection on the start switch should be 0 ohms.
A different connector on the switch should go to 0 ohms when the button is pushed. Looks like it might be light blue (LBU).
The rest of the readings require that the start button be pushed and held.
Both sides of the thermal fuse should be 0 ohms.
4M on the motor should be 0 ohms
5 M on the motor should be around 2 ohms.
W on timer switch 4 should be ~2 ohms.
T on timer switch 4 should be ~2 ohms.
LBU at the door switch should be ~ 2 ohms
White wire of the door switch should be ~ 2 ohms
Neutral at the line cord plug should be ~2 ohms.

There that is the complete motor start circuit.

In case you do not have it here is the install sheet for this unit.
It shows the difference between 3 and 4 wire hook ups.
http://www.whirlpool.com/digitalassets/MLPDF/Installation%20Instructions%20-%208577188.pdf

Although not reconnecting the ground strap from Neutral to the machine frame/case when going from 4 to 3 wire should not cause your problem. I would check that this was done as it is a safety issue if the case is not wired to Neutral on a 3 wire circuit.

Since you feel that it may be a Neutral problem you could follow the same troubleshooting but start from the Neutral side.

[COLOR="Blue"]5 M on the motor should be around 2 ohms. Got nothing here, bad timer neutral?[/COLOR]

So from L1 to 4M you got 0 ohms but from L1 to 5M it was infinite ohms.
Is this correct?

If yes then your motor is blown.