Connecting to Bloomberg Server

I downloaded bloomberg api:blpapi3.jar, I uesd javaaddpath to load it into Matlab.I have Bloomberg terminal on my pc.In matlab I wrote c=blp to build connection. This has been working for a week, it stopped working today. when I tried c=blp it showed a cmd window: Primary Host is up! Anyone know how to slove it ? I really dont understand why it was working yesterday but stop working today. thanks!