why cant i connect to the router from one of my computers?

this is a really weird issue that has be baffled..

my computer running windows 7 all of the sudden cannot connect to my router via ethernet whilst other computers are able even iphone via wireless.

heres where it gets confusing when i connect my older router it works fine.

i have reset ip stack, winsock, cleared arp cache, updated NIC drivers to no avail.. i cant figure out if its something on my PC or the router.

i have configured addresses manually.

any ideas?