Hello,
follow the procedure described in this document:
CISCO CATALYST 3550 SERIES SWITCHES
Troubleshooting
Recovering from Corrupted Software
http://www.cisco.com/en/US/partner/products/hw/switches/ps646/products_configuration_guide_chapter09186a00800c9ff0.html#xtocid2
If you cannot access the link, here is the relevant information from the document:
Recovering from Corrupted Software
Switch software can be corrupted during an upgrade, by downloading the wrong file to the switch, and by deleting the image file. In all of these cases, the switch does not pass the power-on self-test (POST), and there is no connectivity.
This procedure uses the XMODEM Protocol to recover from a corrupt or wrong image file. There are many software packages that support the XMODEM protocol, and this procedure is largely dependent on the emulation software you are using.
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Step 1 Connect a PC with terminal-emulation software supporting the XMODEM Protocol to the switch console port.
Step 2 Set the line speed on the emulation software to 9600 baud.
Step 3 Unplug the switch power cord.
Step 4 Press the Mode button, and at the same time, reconnect the power cord to the switch.
You can release the Mode button a second or two after the LED above port 1X goes off. Several lines of information about the software appear along with instructions:
The system has been interrupted prior to initializing the flash file system. The following
commands will initialize the flash file system, and finish loading the operating system
software:
flash_init
load_helper
boot
Step 5 Initialize the Flash file system:
switch: flash_init
Step 6 If you had set the console port speed to anything other than 9600, it has been reset to that particular speed. Change the emulation software line speed to match that of the switch console port.
Step 7 Load any helper files:
switch: load_helper
Step 8 Start the file transfer by using the XMODEM protocol.
switch: copy xmodem: flash:image_filename.bin
Step 9 After the XMODEM request appears, use the appropriate command on the terminal-emulation software to start the transfer and to copy the software image into Flash memory.
HTH,
GP
