Modem gets no dial tone only at home !

I had to change a burnt power supply and reformat my disk and reload W98SE. My first HSP 56 Micromodem internal modem got no dial tone at home. I have bought an other one, a not winmodem, 3com USR 56k PCI: no dial tone . I tried elsewhere (two locations) to change phone line : my modem connects perfectly. I tried two laptops back on my home phone line: they connect perfectly. I tried two others internal modem aboard my PC with my home line: they don’t connect (no dial tone). I try the laptop through the internal modem: it connects. I (and few colleagues) am running crazy… Any help how to check a phone line ?