Internet Gets Disconnected when Ethernet cable Plugged in

i'm using PTCL 4MB connection, the Modem is 1020-25 by PTCL

i been using wifi since long without any issue.
Bought a PC yesterday, Plugged in Ethernet cable and internet gets disconnected, Unplugged the cable and restarted the router and internet is working fine.
What could be the problem ?

check if there is some kind of current/earth in the casing, which can interfere with wire.

try to use Ethernet in different laptop/pc other than the one causing the prob.

other than that it will be a router issue or else, can't diagnose until see it.

If nothing helps you can get a wifi card or usb dongle for your PC to use the wireless interface.

You phone line or one of the lan cable is damaged. This happened with me.

I was having the same issue when I connected my wireless router to the dsl modem. Whenever I plug the adaptor the dsl goes off. The problem was causing by a bad/low quality power adaptor. So please check the lan cable or possible some issue with earthing.