This basement has a crack running horizontally along the block concrete wall. There's also a stair-step crack on each end of the horizontal crack, and the wall is bowed in about 1 in. You can't handle this cracked wall by simply filling the crack and finishing off the basement. If you only had the stair-step cracks, you could go ahead with your basement finish work, because that type of crack is a normal sign of settling. Stair-step cracks may cause cracks in other walls above or a door to rub, but they don't compromise the strength of the foundation.
However, the horizontal crack that has bowed the wall inward is the sign of a severely weakened wall that can fail. Even if it has been stable for awhile, it can no longer reliably support the load it's supposed to carry. If your basement has this problem, our advice is to ask a local general contractor or building official to direct you to a structural engineer who can examine the wall and surroundings and suggest the correct method to reinforce the wall.