Kasus ini terjadi terhadap laptop saya, compaq CQ40, ketika ada slot MMC, tapi nda bisa baca (muncul drive-nya). Kemungkinan penyebabnya adalah daemon tools yg saya pakai, berikut adalah solusi-nya dan sudah saya praktekan, alhamdulillah berhasil :
…..
There are reports that a failed intallation of the Daemon Tools V4
caused this behavior.
Another thing to try:
Create a system restore point first…
Then open Regedit and go to
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\MountPoints2
Delete or rename the whole MountPoints2 hive.
Then go to
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
Delete or rename the whole MountedDevices hive.
Reboot and hope 
Then Windows will reassingn all letters and maybe it will assing
letters for USB drives again.
…..
taken from : http://groups.google.com/group/…..hread/d80bc554d9df03e5
