Unable to install Windows 10 on Precision T3500

2009 PC, (as-old-as)

has no UEFI, so it's easy.

id try to remove all SATA devices first.

and prove (make it)  boot to the USB install stick.

use another PC to make the stick using the MS builder for w10, use nothing else and 8GB + stick.

if the stick is not new, erase it first. the run the builder.

then tell the MS builder both (32/64bit) when asked, on and empty erased stick.

in bios turn on legacy mode, for USB;. And the BIOS USB page make sure all ports are enabled. next.

and use the same boot key F9?  (or what it is)

to get the DELL boot on the fly menu.  seen in your  post.

get the boot stick working first. and a new RTC coin cell battery  if below 2.9vdc.

if the stick still fails test the STICK on PC#2 to see if the stick really does boot. (just to the first MS window PE)

always make sure the stick really works first.

booting to external DVD drive I do not think this ever worked. (internal DVD yes, sata and using only the MS builder for W10)

that old wdc2500 is 250GB relic,  it needs to be fully tested before any W10 is loaded on it,

if it fails smart tests, w10  will fail 10 times loaded.  never install any OS and not test the HDD First.

even run crystaldiskinfo.exe  and then erase it first, 100% or these ways of many.

That is all for now....

Hi @lorenzo.milesi,

Is the drive you want to load to formatted and does it have no other OS (operating system) on it?

Also, have only the HDD or SSD you want to load plugged in during loading.

I think booting USB at least wasn't straightforward on the T3500.  Try googling for something like "unable to boot USB on Dell T3500" or Dell T3500 plus the error message you got.