Start by getting the car up on jack stands, so you can see what is going on.

First step is the clutch disengaging?.....does the clutch fork move back when you depress the clutch................I actually had one stick on a Volvo rally car..........thought the clutch was gone but it wasn't............bunch of dirt packed up the bell housing.

Next step put it in gear while the car is off the ground...............if the wheels spin it's the clutch is likely done, with no load you can gently accelerate to see if the wheels spin a little faster..........no need to go faster than 10 mph on the speedo.

Then work back through the drive train but if somrthin in the tranny or rear end were broken it would likely make nasty noises.

Also make sure the car really is in gear, with the car off the ground and the motor off you work the wheels back and forth then try put it in gear.

Tom