Originally Posted by Rodney

Sewing machine oil inside and out. Wipe it down with some sewing machine oil. Other oils are too heavy or can gum up or both. If it has plastic gears, no oil on those. Some plastics are sensitive to oil and can be damaged by it.
Take the top off and oil everything that is metal and looks like it should move. Do the same to the bottom and inside the nose. Take the bobbin and bobbin case out. Most machines it's easy to remove the hook too and a lot of times you will find a thread jam behind there making things stick.
With a little time and patience you'll get it freed up. Try gently rocking the wheel back and forth. Any movement is good and will help the oil soak in. It didn't freeze up overnight, you can expect it to take some time to get unstuck.
Rodney