USB external harddisk without device name

Today, I have an USB external harddisk connected, but it is not detected by my PC without device name (such as /dev/sdxx) . IRC guys help me to troubleshoot and I learned a new command to check if USB module is loaded.

debsrv1:/home/william# lsmod | grep usb
usb_storage 94528 0
scsi_mod 160760 5 usb_storage,sg,sr_mod,sd_mod,libata
usbhid 45792 0
hid 41792 1 usbhid
ff_memless 9224 1 usbhid

lsmod — program to show the status of modules in the Linux Kernel.

and finally, I found out the issue is due to my mistake: using the wrong power adapter for my USB harddisk. :P