DSL Problem

Definitely,
We have 2 computers inside my house connected to DSL. My main laptop works perfectly however the other computer(which offers the modem.. IDK why many people didnt install it to the main pc nonetheless anyways)sometimes has troubles loading pages in FFox. I called the particular guy that put in it and he said the fact that ‘sync’ light on the modem should become constantly lit and never flashing. I have to restart that computer before it’ll load the internet pages in firefox. I dont know very well what may be triggering this and I became wondering if you guys often have the solution to help my problem THANKS for any support!