When this happened on my Berkie last year, I found that a data cable female x female splice had shorted out. I could not find the RJ12 connector at the big box stores so ended up stripping ends on both data cables and using a butt splices. I did find a RJ11/12 tester at the big box but you need to locate both ends of the cable to do a test. I found the short trying to locate both ends to do the test.