lan not working

hi,

i have an imac 2012 and i use a lan cable.

The past 6 monds, it worked fine.

But sinds 3 days ago, i do not receive anything from the ethernet cable.

I've tested with a windows laptop and that works also fine..

but with my mac, the router won't give anything of signal..

how do i fix it??

how can this happen??

thanks