Here are your parts, includes a wiring diagram.
Replacement parts for mdb9750aw models | AppliancePartsPros.com

You have 3 devices in the water valve circuit,
The control board', the water valve and the float (overflow) switch

Take the kick panel off and check the overflow switch. It should be activated. If not there may be crud in the float assembly which is holding the float up.

The rest of the checking is easiest with a meter.
Check for 120 volts across the water valve when it should be on.

If you have 120 volts then there is a problem with the valve.
Could be the valve is toast.
Could be that the screen filter built into the input side of the valve is clogged.
Remove the valve from the machine and check/clean the screen filter.
Do not permanently remove it as it is there to keep crud out of the valve which could hold it open and cause a flood.

If there is no voltage.
Check for voltage across the valve and float switch combination.
If there is voltage, then double check by measuring across the float switch.
If there is voltage there then the float switch is toast.

If there is no voltage across the valve and float switch combination, then either you have a broken wire from the the control board, a bag connector or the control board is toast.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.