Just use "blockUI" jquery pluggin. Simply use $.blockUI(); to block and $.unblockUI(); for unblock the screen. For more settings like showing a spinning image under text "Please wait" or any custom CSS, goto below link. Its very easy.
http://malsup.com/jquery/block/#demos[
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Very simple and widely using technique in industry.
Below link for fidler explain how to use it
http://jsfiddle.net/8Mcr6/2/[
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