BEFORE YOU DO ANYTHING...
- MAKE SURE YOU KNOW WHETHER THE GUN IS LOADED. IF YOU DON'T KNOW HOW TO CHECK, HAVE SOMEONE COME OVER THAT KNOWS HOW.
- TREAT THE GUN AS IF IT WERE LOADED.
- KEEP THE MUZZLE POINTED AWAY FROM ANYTHING THAT COULD BE HURT, DAMAGED, OR KILLED IF THE GUN WERE TO GO OFF.
Now with that out of the way, take the gun to a range or to a gun shop and have some folks look it over. Make it clear you are not trying to sell it just yet, but more or less your are trying to figure our what you have. Get several opinions before selling.
And maybe consider keeping it.