problem about boot from gparted on hard disk

Hi all

I have a partition /dev/sda4, which was recognized by vista as H:, and the format was RAW. I reformat this partition using mkfs.ex2(ex3). I also tried mkfs.vfat as well. then mount this partition to /mnt, then unzip the files to /mnt. change grub.conf. but grub could not boot from the selected partition. Then I format this partition to FAT32 in Vista. Then reboot into linux and mount and unzip files again. This time, it boots into gparted perfectly.
But I don’t know the reason? why cant I format the partition from linux?