10 times resetting method works like a charm!
I was using PRS Customizer to flash my 505, and my major purpose was to substitute the default fonts with Unicode fonts (which maybe a cause for the problem, but I remember these fonts can be used without flashing when using methods mentioned here in one of the sticky posts) I found in Hi-PDA forum.
But the process turned my 505 into a brick and I tried unbricking it several times and none succeeded
(Obviously, I forgot to flash my 505 back before I going on with this reflash, this maybe one cause). Right now, my winxp system recognize there is usb drives connected but cannot access them. sony updater also says "connect a 505 to update" though the 505 IS connected by a usb cable. I reset several times and each time it all stuck at starting up screen.