Hi,
Here is a link to the User Manual. If you scroll to p.58 it describes how to restore your laptop to a factory image condition.
Be aware of the following.
1. If the laptop has been upgraded to Win8.1 or Win10 this feature may no longer be available.
2. It will restore the laptop to how it was when it was first built (around year 2010). So to get it up to present day Win7 standard will require a lot of updates.
http://www.lpmanual.com/manuals/dell/DELL_INSPIRON_1564.pdf