I'm trying to fix GRUB on my PC, but I'm running into serious issues doing so. Any help would be greatly appreciated as I'm completely crippled right now. Here is the sequence of events for this PC:

1. Installed Windows 7
2. Split full disk into two partitions (one for win7 and one for multimedia)
3. Long time passed
4. Split one of the partitions into two again
5. Installed Ubuntu 11.04 on new partition
6. A little time passed
7. Windows 7 acting up, reinstall
8. Ubuntu GRUB gone
9. Tried restoring GRUB by mounting and grub-install from live USB
10. Tried switching to a live CD instead of USB (thinking it might be the drive)
11. Now I don't see GRUB and I'm getting "input/output" errors

An example i/o error:

ubuntu@ubuntu:~$ sudo fdisk -l

Disk /dev/sda: 750.2 GB, 750156374016 bytes
255 heads, 63 sectors/track, 91201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xbe86aff6

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1       48727   391393280    7  HPFS/NTFS
/dev/sda2           48727       77063   227612647+   7  HPFS/NTFS
/dev/sda3           77063       91202   113566721    5  Extended
/dev/sda5           77063       90622   108908544   83  Linux
/dev/sda6           90622       91202     4657152   82  Linux swap / Solaris


ubuntu@ubuntu:~$ sudo mount /dev/sda5 /mnt
ubuntu@ubuntu:~$ sudo grub-install --root-directory=/mnt /dev/sda
mkdir: cannot create directory `/mnt/boot': Input/output error
ubuntu@ubuntu:~$ cd /mnt
ubuntu@ubuntu:/mnt$ ls
ls: cannot access etc: Input/output error