Try this page for more information.

The PC won't recognize the USB stick with the ISO on it. Yes, I made it correctly. 

You have to boot to the usb drive and select custom install. You cannot boot to the new drive until you install windows. If you made the thumb drive correctly by burning not copying the iso file to the thumb drive, boot to it.

How to Install Windows 7 From USB (Flash Drive, Ext HD) (lifewire.com)

All drivers are in a single cab file.

https://dl.dell.com/FOLDER01940139M/1/T3600-win7-A06-K61NC.CAB

Contents of the cab must be extracted into a folder

https://www.7-zip.org/download.html

HOWEVER you must use a DELL 2016 skylake or newer image DVD.

USB install is not supported.

https://www.dell.com/support/kbdoc/en-us/000148150/how-to-install-the-storage-controller-f6-driver-during-the-windows-installation-setup-process

skylake dvd