Linux password

You should be able to use a Live CD...  See http://www.howtogeek.com/howto/linux/reset-your-ubuntu-password-easily-from-the-live-cd/

I have a thumb drive so will that work?

It zorin can I do that via command line?

As long as you can boot the system, and as long as you can mount the partition (/) of the drive, you can navigate to the etc/shadow and modify the login.

Do you have a limited user that you can login with and then use sudo to elevate your rights?

that's just the problem. We don't know the passwords for the limited user either.

Ok, the only option is to use a liveCd or USB stick to boot the sysytem and the mount the partition that has the etc directory and edit shadow to replace the current password with a new one.
The complexity depends on how your current system partitioned/setup.
I.e. does the system have raw partitions, lvm based partition or software raid with lvm overlay.
In the case of software raid, you must have info on which disks/partitions make up which volume to avoid data corruption.
RAID 5 groups will cause the most difficulties.

When dealing with software raid, you have to use mdadm, and other tools to be in a position to identify array members.

NO raid just a PC but I'll try thanks.

if this is raw partitions or LVM only,
fdisk -l will tell you which drives are partitions how.
raw partitions you can simply do
mount /dev/sdax /mnt and look to see what is there.
if LVM partitions are referenced,
you would need to use pvscan, vgscan,lvscan
lvmdiskscan
to see what LVM partitions there are and then do the same
mount /dev/volumegroup/logicalvolume /mnt and look around there for etc.

Question needs to be close machine was totally reinstalled.