Grub does not have a concept of C: or F: or anything like that. The only thing it knows about are partitions. So formatting the partition shoudn't have changed anything.
However, you said your drive letter changed from C: to F:. Am I right in assuming you changed your main Windows hard drive. In other words, you now have a new C: drive you boot from? If you did, then that's the problem. Grub was installed in the boot block of your OLD C: drive. To get the dual boot back, you'll have to re-install Grub onto your NEW C: drive. To be technically correct, you need to install Grub onto the drive you boot from (which is probably your new C
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To do that, you'll need your boot disk to get into Linux. IThen you'll need to verify your grub.conf file: make sure all the partitions for your new drive match up correctly. Then, I believe the command is 'grub-install <drive>' as in grub-install /dev/hda.