Downgrade to Windows 7 Clean

Hi All

I got a computer for a customer that had Windows 10 preinstalled, mainly because I cannot find Windows 7 Machines very easily and for a decent price.  I figured I would just downgrade it to Windows 7 like I have done so many times in the past.....

This is an Acer Aspire T

I went into the BIOS and Under Authentication, I disabled Secure Boot
I also Went to the Boot Tab and Switched Launch CSM to Always Launch instead of Never
I changed the First Boot Device to the DVD drive
I also enabled the Boot Menu

Ive tried with the on board DVD drive
Ive tried with an external DVD drive
Ive tried with another internal DVD drive connected to another SATA port

Every single time I get nowhere....

I cannot get this machine to Boot from a CD no matter how hard I try.  I must be missing something.  I know this Disc works.

Anyone able to assist?

Thanks