Window blind mechanisms often pinch the cords and prevent you from lowering them. The cords, generally two to three, thread over a pin and beneath the pawl -- a small metal roller with teeth to grab the cord -- inside the lock mechanism in the head rail. The pawl moves up and down along a slotted track to lock or release the cord and lower the blinds. When the pawl locks in place, you can't lower the blinds.
Tug on the Cords
Tug the cords gently that raise and lower the blinds to loosen the blinds and lower them. Pull the cords to the left toward the center of the blinds and parallel to the head rail, putting tension on it as you lightly tug. This should let the pawl fall to its lowest position, creating the space between the pawl and the pin to release the cords and lower the blinds.
Remove the Window Blinds
When tugging the cords to the center of the blinds doesn't lower the blinds, remove the blinds from the brackets. Lift up and out, depending on your bracket configuration, to remove the blinds from the window. Set the blinds on a tabletop or countertop so that the lock mechanism with the open top of the head rail is accessible.
On the right side of the blinds in the head rail, note how the cords thread through the lock mechanism. With a flat-bladed screwdriver, press down on the pawl with the blade perpendicular to the roller to move it to its lowest position in its slotted track. The pawl or teethed roller is suspended on two pins that run in a slotted track at the front and back of the mechanism; sometimes the pawl gets stuck at the top because of extra pressure applied to it when tugging the cords to the right, away from the window to lock the blinds in an open position.
A pawl that has one end up in the slotted track and the other end down needs realignment to get it to release. Gently push up on the side that is in the down position, and then press down on the side that is in the up position to level the pawl evenly. The roller can skew like this when the blind cords are not pulled equally, causing one cord to lift one end, while the other doesn't move the pawl at all. Once you return the pawl to its lower position, apply a bit of lubricant to the pins to ensure they move smoothly on the track.
Check the cords that run through the lock mechanism to ensure they are not knotted or bunched up, as this will cause the pawl to get stuck as well.
Reinstall the blinds; raise and lower them several times to ensure they work correctly.