Are you loading a grub reinstall from the USB and is it version 1.99?

I'm going to suggest that you try a GRUB reinstall - normally a dangerous procedure, but you have nothing to lose.

I'm suggesting you do the following (from a USB boot):-It could be useful to send to the forum a list of your / directory, which you can do by sending the output ofFor comparison purposes only, it will look very roughly something likeIf the directory /mnt/etc/grub.d/ contains less than 5 or 6 files, STOP.

If the file /mnt/etc/default/grub is missing or empty, you probably ought to STOP.
otherwise
[ I'm assuming your / is on sda1 ]

Make sure you spell everything exactly as written.

Then try booting from disk.......

heres the result

mint@mint ~ $ ls -lh /mnt
total 112K
drwxr-xr-x 2 root root 4.0K Sep 12 21:55 bin
drwxr-xr-x 3 root root 4.0K Sep 12 21:53 boot
drwxr-xr-x 2 root root 4.0K Sep 12 21:53 cdrom
drwxr-xr-x 4 root root 4.0K Jun 24 10:20 dev
drwxr-xr-x 144 root root 12K Sep 12 21:55 etc
drwxr-xr-x 3 root root 4.0K Sep 12 21:52 home
lrwxrwxrwx 1 root root 33 Sep 12 21:53 initrd.img -> boot/initrd.img-3.13.0-24-generic
drwxr-xr-x 25 root root 4.0K Sep 12 21:55 lib
drwxr-xr-x 2 root root 4.0K Jun 24 09:57 lib64
drwx------ 2 root root 16K Sep 12 21:49 lost+found
drwxr-xr-x 2 root root 4.0K Jun 24 09:57 media
drwxr-xr-x 2 root root 4.0K Apr 10 22:12 mnt
drwxr-xr-x 3 root root 4.0K Jun 24 10:12 opt
drwxr-xr-x 2 root root 4.0K Apr 10 22:12 proc
drwx------ 3 root root 4.0K Sep 12 21:53 root
drwxr-xr-x 12 root root 4.0K Jun 24 10:25 run
drwxr-xr-x 2 root root 12K Sep 12 21:55 sbin
drwxr-xr-x 2 root root 4.0K Jun 24 09:57 srv
drwxr-xr-x 2 root root 4.0K Mar 13 2014 sys
drwxrwxrwt 2 root root 4.0K Sep 12 21:54 tmp
drwxr-xr-x 10 root root 4.0K Jun 24 09:57 usr
drwxr-xr-x 11 root root 4.0K Jun 24 10:26 var
lrwxrwxrwx 1 root root 30 Sep 12 21:53 vmlinuz -> boot/vmlinuz-3.13.0-24-generic

i count more than five things there so i assume its safe

heres the grub install results

sudo grub-install --root-directory=/mnt /dev/sda
grub-probe: error: failed to get canonical path of `/cow'.
Installing for i386-pc platform.
Installation finished. No error reported.
mint@mint ~ $ sudo umount /mnt

and no luck still invalid extent

It wasn't able to work - it's that The good news is that you appear to have a proper Linux setup.
The previous procedure can be done with a few extra commands to avoid the /cow problem. I've never had to do it though.

You might like to read http://community.linuxmint.com/tutorial/view/245, and follow the second comment which claims to evade the /cow problem.

Good luck!

mint@mint ~ $ sudo mount /dev/sda1 /mnt
mount: /dev/sda1 already mounted or /mnt busy
mount: according to mtab, /dev/sda1 is already mounted on /mnt
mint@mint ~ $ mount --bind /proc /mnt/proc
mount: only root can do that
mint@mint ~ $ mount --bind /dev /mnt/dev
mount: only root can do that
mint@mint ~ $ mount --bind /sys /mnt/sys
mount: only root can do that
mint@mint ~ $ sudo -s
mint ~ # mount --bind /proc /mnt/proc
mint ~ # mount --bind /dev /mnt/dev
mint ~ # mount --bind /sys /mnt/sys
mint ~ # chroot /mnt
mint / # grub-install /sda1
Installing for i386-pc platform.
grub-install.real: error: cannot find a GRUB drive for /sda1. Check your device.map.
mint / # -ls
No command '-ls' found, did you mean:
Command 'ils' from package 'sleuthkit' (universe)
Command 'tls' from package 'python-tlslite' (universe)
Command 'als' from package 'atool' (universe)
Command 'hls' from package 'hfsutils' (main)
Command 'jls' from package 'sleuthkit' (universe)
Command 'bls' from package 'bacula-sd' (main)
Command 'i-ls' from package 'integrit' (universe)
Command 'fls' from package 'sleuthkit' (universe)
Command 'ols' from package 'speech-tools' (universe)
Command 'ls' from package 'coreutils' (main)
-ls: command not found
mint / # ls
bin dev initrd.img lost+found opt run sys var
boot etc lib media proc sbin tmp vmlinuz
cdrom home lib64 mnt root srv usr
mint / #

that happened for some reason

Reboot from your USB.
All those GRUB reinstall commands should be prefixed with sudo.

The grub-install command was wrong, should've been
Also OP was already operating as root.

mint@mint ~ $ sudo -s
mint ~ # mount /dev/sda1 /mnt
mint ~ # mount --bind /proc /mnt/proc
mint ~ # mount --bind /dev /mnt/dev
mint ~ # mount --bind /sys /mnt/sys
mint ~ # chroot /mnt
mint / # grub-install /dev/sda
Installing for i386-pc platform.
Installation finished. No error reported.
mint / # update-grub
Generating grub configuration file ...
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
Found linux image: /boot/vmlinuz-3.13.0-24-generic
Found initrd image: /boot/initrd.img-3.13.0-24-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
No volume groups found
done
mint / #

i think it may have worked, i'll try rebooting

nope, still getting invalied extent

Are you sure, that grub didn't install to your usb instead of the hdd? Try booting hdd from usb. If that works unmount & remove usb, then try grub-install.

well according to gparted, sdb is the name of the memory stick, and sda is the name of the hard drive which is what i mounted to as seen by my first line of text, so i'm not sure how it could have installed to the usb if its supposed to be mounted to the hard drive

but regardless i'll try it anyway, so how exactly do i boot my hdd from a usb?

If grub is on it you will know it have you booted the usb since the las time you ran those commands?

yes, i'm running in live boot right now

If this is an external drive, is the internal drive still connected?

well i have everything important on my internal drives so i unplugged the data cable so i didn't accidentally overwrite the drive when i installed, i'm not really sure why it matters though, shouldn't linux be able to install fine on its own?