Faucet Stem stuck in the faucet body
There are a couple common reasons why the valve(s) might be locked up:

You reinstalled the valve in a position other than wide open. If the valve stem is in the closed or partially closed position (see pic below of valve that is not in the fully open position) when installed, the stem could strike the seat before the valve-body is fully tightened. This could destroy the new washer you replaced, could bend or otherwise damage the stem, could damage the seat that the washer seals against, and could destroy the worm threads on the stem and/or inside of the valve body that drive the stem in and out when you turn the handles. SOLUTION: remove the entire valve again and inspect for damage and proper operation prior to reinstalling with the stem in the fully retracted/wide open position.



You inadvertantly tightened the packing nut during your repair efforts. The packing nut is the smaller brass nut just outward from the valve body where the stem protrudes from, you can see it plainly in your first picture. Over-tightening the packing nut can make the stem difficult to turn (but undertightening it will cause a packing leak).