Stuck in GRUB Shell — Cannot Boot Windows USB or Enter BIOS (Dell XPS 13 7390)

I'm facing a frustrating boot issue on my Dell XPS 13 7390. Here's the full situation:

🔹 Background:

• My laptop runs in UEFI mode with Secure Boot disabled.

• GRUB is installed (likely from a previous Linux installation).

• I’m trying to boot into a Windows 10/11 Setup USB to reinstall or repair Windows.

🔹 Issue:

• When I power on and press F12, the system shows the "Entering Boot Menu" loading bar but still goes straight into the GRUB shell.

• It refuses to enter BIOS or the Boot Menu under any condition if a bootable USB is connected.

• GRUB shell is the only thing that loads.

🔹 What I’ve Tried:

1. Windows USB:

   • Created with Rufus (GPT, UEFI, FAT32 and NTFS variants).

   • The USB is detected in GRUB (ls confirms it), and I can see /efi/boot/bootx64.efi.

   • When I try:

     bash

     Copy Edit

     chainloader (hd1,gpt1)/efi/boot/bootx64.efiboot

     I get: "cannot load image", even though the file is present.

2. Old Windows on NVMe:

   • If I boot without the USB, I can chainload and successfully boot into my existing Windows installation:

     swift

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     chainloader (hd0,gpt1)/EFI/Microsoft/Boot/bootmgfw.efiboot

   • However, after attempting to chainload the USB once, even booting the old Windows gives “cannot load image” — until I reboot.

3. BIOS Access:

   • When USB is plugged in, I can't access BIOS at all (F2 or F12 → always drops to GRUB).

   • Even when USB is first in boot priority, it still goes straight to GRUB shell.

4. Rufus USB:

   • Rufus-created USB (GPT + UEFI) does show up and partially boots but gives:

     java

     Copy Edit

     Load unsupported (3)

   • Same with NTFS and FAT32 variants.

🔹 Conclusion:

• It feels like GRUB has hijacked booting, and the Dell UEFI firmware refuses to override it.

• Chainloading the USB bootx64.efi fails with cannot load image.

• BIOS cannot be entered when USB is present.

• After trying to chainload USB once, GRUB breaks the context and can’t load any EFI file until reboot.

• I suspect a firmware/NVRAM issue or UEFI boot context conflict.

🔹 What I Need:

• A reliable way to:

  • Boot directly into BIOS (even with USB inserted).

  • Reset NVRAM/boot entries so GRUB doesn't override everything.

  • Successfully boot into Windows Setup from USB on UEFI.

Let me know if more hardware info is needed. Thanks!