|Dear sohail khan ,|
Seems some settings are misconfigured.
I would like you to follow below steps (I know u have done this but please verify )
I am 99.99% sure , this will help you.
-On the computer with 2 NIC, one NIC ip is from ISP (DHCP) and 2nd is to be choosed by you.
1 ) assign this Ip to ur 2nd NIC.
IP = 192.168.10.1
subnet = 255.255.255.0
gatway = 192.168.10.1
DNS = 192.168.10.1
( I believe internet connection sharing is already enabled on first NIC)
2) on the client compuers assign below IPs.
IP = 192.168.10.2 or 3 or 4
Gatway = 192.168.10.1
Here, gatway is importent.
now, check the connection,
It should work now.
If case no then pls post the steps u have doen till now,
remember to type each steps,