If you have ever uploaded an image to a switch that is not supported by that hardware you will be all too familiar with this. Keep in mind these instructions are written for a Cisco 3750x switch, other switches may be different. Now looking at the switch on the console it appears to be booting fine as the image loads but then you are greeted with a message similar to the one below.
So at this point it will continue to loop through post, decompressing the image and puking at you. So we know we have a bad image on the switch and we need to boot to a different image, but we keep going through this loop and we cant get to the ‘switch:’ prompt. In order to get to the ‘switch:’ prompt follow the directions below
To access the ‘switch:’ prompt you will first need to unplug the switch from power.
Then press and hold the ‘mode’ button on the front of the switch, you can find it next to the USB console port on the far left of the front panel, see the picture below.
While holding the mode button restore power to the switch and continue to hold the mode button for about 20 seconds or so until the ‘SYST’ light flashes green 3 times and goes dark.
This will trigger your switch to boot into the ‘switch:’ prompt and you can recover your switch by loading a new IOS onto it directly from the ‘switch:’ prompt and booting, or booting to a USB and doing an image recovery.