Yamaha xv250s virago 2001. Bike has stood unused for months in cold weather. Engine runs ok but clutch won't allow to put in gear. Cables and levers seem to operate ok and adjustment hasn't helped. Please help me.

The clutch master/lever has a safety switch that tells the bike if the clutch lever is in (no power to rear) or out (power to rear). After almost 30 years this switch may have failed, making the bike think that the clutch is engaged regardless of lever position. If you have a multimeter you can test the switch yourself. Since the bike starts properly in neutral (also a safety feature) then the clutch lever switch is your most likely problem. Your bike might also have a side stand switch like mine. It functions much the same way, if the side stand is down and the bike put in gear it will kill the engine.

MGM

If you are at idle, in neutral, with the clutch lever pulled all the way in, and you shift into gear and the engine dies, it is likely the switch at the clutch lever. When they fail the bike does not get the signal that the clutch is disengaged and it is safe to shift into gear. Have that switch checked. Some bikes also have a side stand switch, make sure your side stand is always up before putting you bike into gear.

MGM

you could try riding the bike in third or fourth gear with the clutch lever pulled in and accelerate

The Clutch on some bikes will disengage the starter motor. Yamaha will not allow you to engage gear when the side stand is down. Hope this gives you some idea

There are a few safety interlocks on most Yamaha street bikes.
The starter circuit will only operate if:
the bike is in neutral and the neutral light indicates this OR
if the bike is in gear (or neutral light not showing) you must have the clutch pulled in and the sidestand must be up (there is a clutch lever switch and a sidestand switch )
The engine stop switch "kill switch" on right handlebar has to be in the RUN position to allow starter cranking.

Check your kickstand switch. It will not allow the engine to run in gear when you release the clutch lever. It may be gummed up.

check your idle speed.you should have about 1 cm of free play in the lever.also does it start up agian and are you able to drive it if not check your side stand switch