Top loader? Front loader? Make? Model? Age? Can you tell if the motor is running or not?
In the mean time, I will assume a top loader, and my first thought would be the belt. Are there any indicators that might confirm this, such as a squeal or burned smell? If not, I'd still go there, as they are relatively small, so often the fact that they are bad is not immediately obvious. With the power off, you can feel the belt by reaching under the machine. If it does turn out to be the problem, replacing them is relatively easy. The hardest part usually is finding the two screws that hold the bottom of the front panel in place; they're often tucked under a roll in thee metal, for concealment. After that, pull the front out, remove it from the clips that hold it at the top, and you can get to the belt.
The other easy possibility could be a the lid or door switch, which is also relatively easy to replace, but you will want an ohmmeter to diagnose it, and my experience has been that they either work, or not, with nothing in between.
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