hai letto le faq su xda?
prova così...
2.3 External SD card not mounting to USB / Cannot see in file explorer
Location of External SD Card - Look for the external_sd folder - sdcard/external_sd
If there is not external_sd folder, MAKE ONE, then reboot.
If your external sd card is still not detected and you have created the external_sd folder, you most likely have the Gingerbread 2.3.3 bootloaders.
Flash back to Froyo using EZBase 2.0 ROM and then follow instructions from 1st post
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