WIN PE is a slimmed down thing. At no time would I expect it to give me full chip and USB support.
And there's the rub. You will find machines it works on then not.
Parting idea. Check the BIOS for LEGACY USB support.
Second parting BIG idea. I don't use WIN PE anymore. Why? Read:
i can boot my new notebook 250 G4 from bootable WIN PE USB stick. it boots off usb and goes to command line happily. Now when i go to DISKPART and type List Disk or List Volume, it doesnt list my USB stick. it will show only my hard drive and its partition and CD drive. i need to get on to this USB drive so i copy my image.wim file from it so i can apply it to my this new laptop. This USB stick is working absolutely fine on 3 other laptops (hp and dell).
This new laptop shows this usb in boot option and will boot from it. but when it comes to command line and you want to get on to this usb so you can copy file from thats where the problem comes. it doesnt show in listed disks or volumes.