I have a similarly bricked sheevaplug. I was attempting to update uboot when it occurred. Green led solid, no blue led. Yellow and green leds on nic port ( I have sheevaplug connected to my LAN ) are on solid most of the time, but at intervals, yellow led blinks about 10 times.
Any help would be appreciated.
SUCCESS!!! After modifying runme.php of sheevaplug-installer-v1.0, I was successfully in reviving my sheevaplug. The major modification for me was to remove root from the line 43 which required user="root". I just made user ="".
I still have some work to do but the blue led is functional as well as Uboot.
Hope this helps someone else in their un-bricking