Right at the moment I'm sitting in one of our wireclosets, watching an c3750 (hopefully) recovering its mind to its old function and behavior - through an XModem transfer of its current IOS. Because of an power failure on our campus the unit actually "bricked" - the flash system became corrupted and the unit did end up in the ROMMON Mode "switch:".
Thats pretty bad - but not as bad as we couldn't fix it.
1. Connect to the console port with the usual settings of 9600 Baud, 8 Bit, No Control, 1 Parity.
2. Power up the switch and hold the mode button until it comes to the ROMMON - and yeah, if you did delete the IOS or your switch is bricked like mine, it does come to this point by its own - no need to do that.
3. Before doing anything, check the file system with fsck flash: - if that gives error you should really format the flash - as it is corrupted and theres no need in flashing it a second time - because the new IOS will become bricked as well (I figured that out myself some minutes ago...). So if you don't have any important data like an non-saved config on that flash, erase it with format flash: and reboot the switch with reset. Test again with fsck, if there are still errors: Forget the switch, send it to Cisco. If not, we're going on with our mission:
4. set BAUD 115200
After that you will see nice looking stuff. Set your console to 115200 BAUD as well. Its important to do that as the download of the IOS will take 2-4 hours otherwise. But don't forget to set it back after everything is done with set BAUD 9600
5. flash_init
init the flash
6. load_helper
does load the helper. sometimes useful.
7. copy xmodem: flash:IOSFILENAME
That will start the xmodem download. In Tera Term, klick File, Transfer, Xmodem, Sene and choose the IOS binary. Yes, important: Not an tar File, only the IOS bin.
8. The Download begins, that will take 20 Minutes or so... Some sweet time, but as we know it could be really worse. So kick back, do something useful - like writing this tutorial ;-)...
9. Its done. Enter boot and it will boot. If not its bricked. Don't forget to set back with set BAUD 9600