Unwanted Windows Shut Down

I have checked all connections for tightness. I have a system that reboots every time the phone rings when the system is offline. They have moved the phone into the other room but is still routed to the modem. I tried two ways: I routed it throughthe back of the tower and then as a line branch. I have asked every technician that I can find for a solution. Other than this the system operates correctly. It does not crash, nor lock up regularly. Has anyone had this exact specific problem before and if so what was the solution?