Network cable is unplugged?

this message keeps popping every few seconds,well every second and eventually my router is restarting .if the lan is disabled the router lites are stable.also i encouter this problem mostly during day times, suprisingly not during nites. this is a second router i have changed.i m using a tata indicom broadband connection.its an ethernet cable-Intel(R) PRO/100 VE network connection.i have tried reinstalling, the cable is not damaged. it is annoying it pops every second and literally i can t use the internet at all.any suggestion is welcome