Pre-War, or Pre-64?
The pre-war had a flat safety similar to the 98 Mauser/03 Springfield military safety.
After the war, it was changed to the 3-position side safety.
If that's what it is:
If you have the striker assembly out of the bolt, release the safety and let the pressure off the firing pin spring.
Now pull back on the sleeve and turn it a 1/4 turn either way while keeping the spring from getting away from you.
Now, the safety lever is held in place by a Pin inside the bolt sleeve. drive it out with a proper sized punch.
Now compress the spring loaded plunger with a small flat-blade screw-driver and lift the safety out of the housing.
Not sure what you are going to find but generally, if one of these safety's won't operate, it is not able to clear the cocking piece and cam the firing pin back off the sear.
Might be a burr or wear, or dried grease in the plunger hole.
Or it might be a botched trigger job where someone has cut the sear or trigger too short and isn't holding the firing pin assemble back far enough to clear the safety cam.
Edit: Cross post with Jim Keenan. Looks like I was typing while he was posting!
rcmodel