SKS won't fire?
Things to check out:
Disassemble and take out the bolt and bolt carrier, shake the bolt itself in a forward and back motion. Does the firing pin slide in and out with ease? Do you hear that slight clicking sound as it slide forward and back?
If you don't hear it sliding around, push the back of the firing pin forward. Does it come out of hiding in the front face of the bolt?
If you answer NO to any of these question, you have a faulty or unclean bolt assembly.
Second thing to check out:
Strip the rifle until you have a clear view inside the barrel. (meaning you're able to see from where it chambers all the way out to the business end)
Is the barrel/bore clear?
Is there any obstruction in the chamber or throughout the bore?
Now, put re-assemble the rifle. !!!!!!!!!!!!!!!!!!!!!!!!MAKE SURE THE RIFLE IS UNLOADED BEFORE THIS NEXT STEP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
After assembling the rifle back together, drop the mag to make sure feed path is clear and nothing is blocking it. Ready and #### the rifle = meaning pull the carrier handle back and let it slam forward. And then Make sure the safety is disengaged and pull the Trigger. Do you hear a loud snap/clack?
Keep holding the trigger in the firing position and pull the carrier handle back and let it slam forward again, and SLOWLY RELEASE THE TRIGGER UNTIL YOU HEAR AND FEEL A SOFT CLICK IN THE TRIGGER, this is the safety sear resetting itself! DO YOU FEEL AND HEAR A CLICK?
If you answer NO to any of the second part questions, you have a possible obstructed bore/chamber and the round is not being seated fully therefore the bolt cannot close completely and have blocked off the firing pin from being reached by the hammer OR! your trigger/firing assembly needs to looked at for cleaning and/or replacement.
And lastly, check the ammo. Are the primer's okay? are they falling out? Does the round itself seems a bit moldy or have white powder over it? You have not picked up any rounds from the ground have you?
If you answer YES to any of these ammo questions... well you have ammo issues.
If you want to narrow down the options, contact me by private message and tell me which of the 3 steps have failed and we'll go from there.

hope this helps you out.