Takuya...
DON'T TOUCH YOUR HARD DRIVE ANYMORE OR YOU WILL LOSE YOUR WORK FOREVER.
Follow this steps:
1.- Download "Hiren's BootCD" from
HERE and burn it.
2.- Boot your PC with the "damaged" HDD connected and the BootCD in your CD/DVD drive
3.- Once in the BootCD's menu, go to
Recovery Tools. You will find many useful tools for your problem, but the one I highly recommend is
TestDisk 6.9b. It has helped me to recover partition tables that have been completely wiped out...