My compressor is not turning on the fan is going but the compressor wont kick on what could be wrong it was working fine just an hour ago

Air conditioner compressor will not start. When power is applied to the air conditioning outdoor unit the fan starts, but you hear a sound like the compressor is trying to start, "UGGG"..., for about 5 to 10 seconds and then all you hear is the outdoor condenser fan run. The compressor is locked and will not start. What is happening is the compressor is trying to start, but because the compressor motor is locked it tries to start for a few seconds and then because of the high amperage being drawn goes off on internal overload. The internal overload protects the compressor windings from overheating and burning up. I see this many times during the start of the air conditioning season. Some compressors just have a hard time starting after sitting all winter long. Some compressors are locked up so bad that I can not start them and must tell my customer that they need a new compressor . Many times I can get the compressor started again without having to buy a new compressor using a device called, "Super-Boost." I keep two or three of these on the truck. They have saved many of my customers from having to buy new compressor.