Home phone line disconnects from internet randomly without any reason

Hello,

I was wondering if anyone had any clue as to why or how the internet gets disconnected, When the home phone station flashes a red light where it says Line in- use. we lose connection all together with our router and it seems the router loses it all together when this happens as well. You pick up the phone to answer but all we hear is like fax noise and loud whines. But this confuses us because we don't own a fax machine and nothing other than our home phone and router are connected to the phone line. any answers to fix this problem will be most appreciated thanks. p.s we also checked the line already and nothing is wrong with it.