They are probably still okay but shrimp begin to deteriorate as soon as they die. Sometimes they are "cooked" at sea because the shrimpers can't get back into port fast enough to deliver them fresh to the markets. If you are brave you can fry one up and see what it tastes like. The majority of shrimp sold in markets are frozen defrosted; frequently flown in from Asia. I live close to a port and sometimes the local shrimp are cooked and sometimes they are fresh.

I agree with ChefJune...I very rarely buy cooked shrimp, but even after cooking it myself out it goes after a few days!