Networks

You can copy the bin file from a PC using hyperterminal (and xmodem) to transfer to the device with the console cable. While the official answer is that you need to get the image from Cisco, with some google searches, you will find a copy somewhere on the Internet. Of course if you have another 3750, you can also copy the bin file to the PC using hyperterminal/xmodem. (of course if this were a router it would have a flash-card slot,which is a lot faster way to do this).

http://www.cisco.com/en/US/products/hw/switches/ps628/products_tech_note09186a0080169696.shtml

Such as the free Solarwinds TFTP server

Using Hyperterminal to telnet to switch, at the enable prompt:

show flash

copy the file name of the flash by highlighting it with mouse, right click, copy

copy flash: tftp:

it will ask source filename (paste what you copied above)
it will ask address or name of remote host
it will ask destination filename

then it will copy the flash to the PC

(also good time to make copy of your config)

Now to get the flash back onto the messed up router, you need to connect via serial console cable, connect via Hyperterminal to it, and use Xmodem to transfer it from your PC to the blank device.

http://dataplumber.wordpress.com/2007/06/07/cisco-3750-software-recovery/

Text below copied from link above:

2. Connect to the switch using Hyperterminal at 9600 baud, 8 N 1.

3. You should see a prompt that says ???switch:???. This is the bootloader mode. If you don???t see that, either you???re booted up, and you don???t need these instructions, your switch is properly broken, or you???ve got your terminal settings wrong. Try power-cycling the Catalyst while holding the ???Mode??? button on the front in to get the bootloader.

4. Now downloading the .bin file at 9600 baud is going to take a loooong time (about 2 hours), so we will change the baud rate of the console port temporarily. Enter the command ???set BAUD 115200???. After you enter this command, you will start to get funny characters in Hyperterminal because its baud rate and the Catalyst???s are now mis-matched.

5. Close Hyperterminal and re-connect using 115200 baud instead. You should get intelligible stuff on the screen once more.

6. Type ???flash_init??? to initialise the filesystem. (In our case, this wasn???t necessary)

7. Type ???load_helper??? to load any helper files (in our case there weren???t any since we???d just wiped the flash).

8. Tell the switch to expect a file by Xmodem, and put it on the flash: ???copy xmodem: flash:<filename.bin>??? <<<the name of the bin file goes here

9. In Hyperterminal click Transfer | Send File. In the dialogue box, make sure the protocol is XModem and put in the location of your .bin file. Click ???Send??? and you should see the process start.

10. Once that???s done, issue the command ???boot flash:<filename.bin>??? and the IOS will load up.

http://www.cisco.com/en/US/products/hw/switches/ps607/products_tech_note09186a0080094955.shtml