Staff PM or forced PM ?

[edi67]

mh may be is stupid question but i want know if is possible make this mod:

in my forum i have a lot of users that ignore Pm's Staff , after 3/4 pm i dont understand the reason but them not reply to my pm or staff pm ( and option for enable popup message is enabled ) well i want know if is possible to have one window and remain visible on screen until user reply back or something that if user not reply cannot view the forum or may be one special window ( different from normal pm ) that advise user that pm receiving is FROM Staff-

Every solution is accepted thx