After a software upgrade, the Cisco 2600 series router may boot without errors, but it no longer recognizes the built-in Ethernet/Fast Ethernet ports. This happens when the correct series router is selected, but the incorrect platform is chosen from Cisco Downloads.
When selecting the correct image from Cisco Downloads, be sure to select the correct Cisco IOS Software version for the specific Cisco 2600 series platform. There are different versions for each of these:
Each contains platform specific drivers for the built-in ports.
The router does not recognize the Ethernet ports, so recovery needs to be done from ROM Monitor (ROMmon) mode. Power cycle the router and press Ctrl+Break as it boots. The router goes to the ROMmon prompt.