The handle of the valve moves but the valve remains closed. How do I replace ? It's in a plastic box surrounded by sheet rock and not sure how it connects below the Sheetrock. Is this a do it yourself job or call a plumber?

First try to tighten the handle screw. If that doesn't work, try to remove the handle and see if the internal grooves are worn off. If so, take the handle to HD, Lowe's or ACE and get a replacement. If worse comes to worse, remove the handle and open the valve using a pair of vise grips.

First try to tighten the handle screw. If that doesn't work, try to remove the handle and see if the internal grooves are worn off. If so, take the handle to HD, Lowes or ACE and get a replacement. If worse comes to worse, remove the handle and open the valve using a pair of vise grips.

Thanks for your response. I can't get the handle off. I need to use an Allen wrench and it doesn't budge. Any suggestions?

Soak the fitting with WD 40 and try the allen wrench again. You can make a cheater bar by using a small piece of tubing for more torque.

As a rule washer boxes use 1/2" boiler drains (see image) form shutoffs . Shut the water off to the house and replace the valve. Don't forget to Teflon Tape the threads. Good luck. Tom