I had the same problem with my Sheevaplug (only the Green LED was on, impossible to connect to it). It all happened when I tried to update uboot as described in Martin Michlmayr's HowTo. I used a bad USB Stick and accidentally erased the old uboot without writing the new one to the plug! So I bricked it

The Sheevaplug Installer 1.0 was not easy to handle, as neither the ReadMe, nor the wiki are really up to date. But reading through the different posts helped my finally find a way to unbrick my Plug. I was not able to run Sheevaplug Installer on Ubuntu 10.04, but as the wiki only mentionned Ubuntu 9.04, I set up a virtual machine with 9.04. After installing all the dependencies and changing the MAC Address in my \sheevaplug-installer-v1.0\uboot\uboot-env\uboot-nand-custom.txt file and putting the new uboot.bin to the \sheevaplug-installer-v1.0\uboot folder, I started php runme.php nand as root and got this result:
Error: unable to open ftdi device: device not found
Runtime error, file "command.c", line 469:
**** openocd FAILED
**** Is the mini USB cable connected?
**** Try powering down, then replugging the Sheevaplug
I received the same message on Windows XP, but Windows recognized the Plug, as it asked for the missing drivers when I first connected it to my Windows PC.
As I did not have an idea on how I could find a solution on windows, I continued with Linux (even though I consider myself still a newbie on that OS).
Running dmesg, i got this result:
[11191.190808] usb 2-2: configuration #1 chosen from 1 choice
[11191.271294] ftdi_sio 2-2:1.0: FTDI USB Serial Device converter detected
[11191.271350] usb 2-2: Detected FT2232C
[11191.271409] usb 2-2: FTDI USB Serial Device converter now attached to ttyUSB0
[11191.304381] ftdi_sio 2-2:1.1: FTDI USB Serial Device converter detected
[11191.304414] usb 2-2: Detected FT2232C
[11191.304476] usb 2-2: FTDI USB Serial Device converter now attached to ttyUSB1
So the missing FTDI device was somewhat recognized and connected, and it was not dead.
Running lsusb helped me even more:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 004: ID 0403:6010 Future Technology Devices International, Ltd FT2232C Dual USB-UART/FIFO IC
Bus 002 Device 002: ID 80ee:0021
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
This line was important to me:
Bus 002 Device 004: ID
0403:
6010 Future Technology Devices International, Ltd FT2232C Dual USB-UART/FIFO IC
I remembered reading about the PIDs that had to be changed on newer models (even though my model was older than the one mentioned). And so I replaced this line:
ft2232_vid_pid 0x9e88 0x9e8f
in the \sheevaplug-installer-v1.0\uboot\openocd\config\interface\sheevaplug.cfg file, by this line:
ft2232_vid_pid 0x
0403 0x
6010And after running php runme.php nand again as root, I received this message after a few minutes:
NAND flash device 'NAND 512MiB 3,3V 8-bit' found
successfully erased blocks 0 to 4 on NAND flash device 'NAND 512MiB 3,3V 8-bit'
wrote file uboot.bin to NAND flash 0 up to offset 0x00074000 in 361.948944s
**** U-boot should be up and running now. Open your console ...
The Green AND the Blue LEDs were now working and I was able to connect to my Sheevaplug again! And the version command showed me that the uboot update was also successful! I am now running the Debian installation on my unbricked Plug!
Give it a try, it might be the solution to your problem too

I sure hope so!
BTW: I tried USBDeview with Windows, but while it recognized my Plug as an FTDI device connected to it, it did not give me the same PIDs as lsusb did.