If your system is from a major manufacturer, it will have a procedure and
either recovery CD media or a hard drive partition to return the system to
it's original shipped state. Look through the included documentation for
information on how to initiate the restore procedure. If you purchased the
system from a local store or from mail order; I would suggest you take it
back to the store and ask for a do over or return it according to the mail
order stores returns terms. From your post it seems you obviously have
nothing of importance on the computer, and any attempts you make to rectify
the situation will probably compound the problem.
If the store gives you a problem, and you paid by credit card; return the
computer and let the credit card holder deal with them.
BTW downloading is usually associated with retrieving information or data
from the internet. I believe your use of the "download" reference would be
called installing or running setup.
If you can't return the system, or you have another agenda, see the links
below to help with you dilemma.
Click on or copy and paste the link below into your web browser address box.
I have two installations of Windows/Windows XP on the same partition.......
http://michaelstevenstech.com/xpfaq.html#two
Remove a Dual boot
http://michaelstevenstech.com/xpfaq.html#Remove