|You get an autoassigned ip [169.254.x.x] when set to obtain ip automatically and set to autoassigned if you don't get a dhcp server supplied ip address.|
Assuming this worked before the firmware update this means the cable and computer are fine.
The default lan ip for Linksys is 192.168.1.x. I would suggest setting a static ip on your pc of 192.168.1.3 with no gateway to then see if you can access the router.
You do not repair or reset a router by taking it apart. There is a reset button that you hold in when powering up. But this only resets it to the image loaded in firmware minus any changes you may have made.
Let's hope that all this router needs is the dhcp server configured and engaged which could be why you can't access it now but should be able to one you put a static ip on your pc. Access the router at 192.168.1.1 or review the firmware documents if set differently.