The cord is the tangle-prone culprit behind blinds that won't go down. The first thing to do is make sure that the blinds are lowered all the way down to their lowest position. You can now try and work on untangling them as much as possible, or cut off any remaining parts if it becomes impossible to untangle them. Next time take some measures against getting tangled later on: Cord winders attach onto an individual length while also preventing tangling altogether. There are even pre-made packages specifically designed just for this purpose.