This is another easy problem to solve. Separate into electrical or mechanical causes:
Electrical Issues
First question, "Is the motor (pump motor) running?" A dead motor means an electrical failure such as:
1. Bad lid switch. Very common on the old direct-drive.
Whirlpool Direct Drive Lid Switch
2. Bad timer
3. Bad motor.
4. No power to washer.
For more instructions see individual designs.
Mechanical Issues
If the motor is running or the pump is humming, there is a mechanical issue. There is always the possibility of a kinked or clogged drain hose. Aways check that first. Corrugated hoses are less prone to kinking then solid rubber ones.
Kinked Rubber Drain Hose
1. If the unit has a separate little pump, then the pump or inlet to the pump is clogged. Inspect and fix it. Some of these small pumps will sound like they are working or even worse they will pump fine when you test them and yet they will fail after you leave the job. The pump may be just weak or quits after heating up. If the washer is full of water clamping pliers can be very helpful.
Useful Radiator Hose Clamping Pliers
GE Profile Washer Pump
Cabrio Pump
2. A unit with a belt driven pump has either a clog, sheared impeller or the belt is broken.
Maytag Single Belt Pump
3. A unit with a direct drive pump has either a clog or a sheared impeller.
Amana / Speed Queen Direct Drive Washer Pump