Drive letter disappeared on triple-boot install

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http://superuser.com – I have Windows 7, Ubuntu and Windows XP installed. I first installed Windows 7 than Ubuntu and than Windows XP. My Windows 7 is on C drive, Ubuntu is on a logical drive in my extended partition and Windows xp is on a primary partition F. I have another primary partition E on which for some reason when i installed Windows XP it placed boot.int file on it. I am using grub to boot the three operating system. Yesterday, i reinstalled Windows 7 and after the installation i saw that the drive letter from drive E was gone. I tried to restore but it was not available from the drop down menu in Comput (HowTos)