Dell 5421 - Boot to USB or BIOS with USB Inserted Stuck on Dell Loading Screen

Welcome to the Dell Community  @ebbyit 

Have you run the diags yet???

https://www.dell.com/support/kbdoc/en-us/000181163/how-to-enter-the-built-in-diagnostics-32-bit-diagnostics-supportassist-epsa-epsa-and-psa

https://www.dell.com/support/manuals/en-us/latitude-14-5421-laptop/latitude_5421_sm/m-bist?guid=guid-f469bc97-a2a3-4314-9699-094f5e44f880&lang=en-us

Post your results.

Best regards,

U2

Yes, diags have passed on both machines. I can boot to the USB on other Latitude models just fine but it's just these two that are having the issue so far. I can't find anything on this issue on the web. 

I have been seeing the same issue, but not just on the 5421.
It's also occurring on the 5420 and on the 5330. I don't have any other models to test on.

I noticed the issue start around October 2022.

If you try to boot the laptop with the usb plugged in it will hang on the Dell logo screen.

If you try to boot the laptop with the usb plugged in while pressing f12 it will freeze on the screen as per the first post.

Sometimes a laptop will get stuck in a power cycle boot loop. The laptop starts to boot and then the power light goes out and it reboots a few seconds later.

All laptops have fully updated firmware.

The usb thumbdrives are all created via Rufus to install images created with MDT and will boot perfectly fine on Inspiron laptops and optiplex desktops.

They are all Sandisk Ultra USB 3.0. Some of them were bought brand new when i first noticed the issue because i though they were faulty.

I have one thumbdrive that works just fine with the Latitudes and there is no difference between that thumbdrive and others as far as i can see.

I notice the latest bios for the Precision 7560 fixes what sounds this exact problem.

https://www.dell.com/support/home/en-au/drivers/driversdetails?driverid=24cyp&oscode=wt64a&productcode=precision-15-7560-laptop 

"Fixed the issue where the system reboots repeatedly when USB bootable devices with longer product name and serial number are connected to the system."

After seeing this detail i went and checked my USB thumbdrives and sure enough the one working thumbdrive has a different (shorter) name when compared to the other thumbdrives.

Using wmic diskdrive get Model

The working drive is called "SanDisk Ultra USB Device" and the drives that cause the bootloop are called "USB SanDisk 3.2Gen1 USB Device"

Hopefully this fix can be put into the next bios updates for my laptops.

Any updates to this? Still no bios update available to fix this issue

same problem only with dell products ! 
DELL VOSTRO 
DELL OPTIPLEX
DELL INSPIRON 
someone can help us ???????

Any solution from someone ???

For those who are still struggling with this, I tried a different flash drive per UsernameWasTaken's post and it did solve my problem. I was also using a SanDisk and switched to a Kingston. This is on a 3500 but same symptoms.

Definitely worth a shot. It may require some trial and error depending on what you have available.