LAN card not working sometimes with windows

I have the following scenario

MODEM +  (FE)(Cable A) --> (WAN) ROUTER (LAN)-----(FE)Cable B----COMPUTER

Now i have two LAN cards on computer

1)CARD A is build in Motherbord
2)CARD B is NIC Realteck in PCI Slot

Now

1)If i Plug Cable B in Card A then internet works fine
2)If i plug Cable B in CARD then it does not show anything. Says cable unplugged

then

1)If i put Cable A in CARD A or Card B then internet always works on both

I tried changing cables but same result

What can be the problem

asked Dec 16 '11 at 3:48

100% accept rate

	What connection speeds are you seeing with Card A? Could it Cable B is defective and throttling the speeds on Card A, but Card B is just being proactive and refusing connection? – kobaltz Dec 16 '11 at 3:50
	I tried chnaging ables as well so cable is not problem. Also CARD B works if connected directly from modem. How can i check speed – user105919 Dec 16 '11 at 3:55
	Have you tried selecting different speeds on the Realtek NIC? IE if you have it set to AutoDetect currently, try setting it to Full Duplex and if that does not work, try Half Duplex. Sometimes the autonegotiation protocol that the port is using to set that speed is not compatible with the protocol on the device at the other end and in such cases manually setting it to the correct setting can be all you need. – OG Chuck Low Dec 16 '11 at 4:04
	i tried setting full duplex and half as well but it didn't work – user105919 Dec 16 '11 at 4:15
	Well 105919... I am sorry. I really expected that to work for you. Aside from those options... at this point the only things I can think of are seeing if the router maybe has a firmware update out there of if perhaps the NIC does. Barring that... all I can suggest is to keep trying different speed and negotiation settings. I know my Intel LOM has about 6 seperate settings... try 'em all if you have more than Full Duplex and Half Duplex... :( – OG Chuck Low Dec 16 '11 at 20:21

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