Oh... OK, this is going to be hard, but I will try.

I do not know why that happened to you. Please provide distribution name
and version so that somebody who uses that can help you if I fail.

When you boot with a live CD, which is what I saw you should do, just like
installing a brand new system, you can do a lot of non-traditional things.
What I recommend is that you escape to a shell, as in, a bash or something
like it, that the live CD can provide. Then, type some commands from there.
If the live CD does not have a graphical interface that makes it clear how
to bring up a shell, just type CTRL+[LEFT ALT]+F1 and see if it gets you to
a console. Hit RETURN a few times. If there is a login there, enter "root"
and it should log you in. Now we are ready for some commands.

You can use "fdisk" or "partd" to query the partitions on a disk. It will
typically be /dev/sda for you, as in the first SATA/IDE drive on the system.
Look up online how to use fdisk or partd. It should be able to list the
partitions. Chances are that either /dev/sda1 or /dev/sda2 will be a system
partition, with all the directory structure in it. You will find out how to
"mount" a partition to a temporary mount-point. It should be something like
'mount /dev/sda1 /mnt'
and it will give you access to the entire filesystem under the /mnt
directory on the live-booted system.

Now edit, with an editor like "vi" "vim" or the like, the file:
"/mnt/etc/shadow"
Look online for how to use an editor like "vi" or similar. Be patient, it
will not be easy at first, but it should work. All you have to do is remove
the garbage that will be after your username of the line in the file that
contains it. It will look like this:

danny:kjhsjkhahakjshdfkh::::::

Make it look like:

danny:::::::

where you have two consecutive colons after "danny" which implies an empty
password.

Reboot the regular system and just log in without a password.