Dell Venue 8 pro (5855) bootloop + no input bios/bootmenu

Hi Guys,

I have this weird problem with my Dell Venue pro 8 (5855) tablet.

Last week I updated drivers after a fresh Windows installation. After the mandatory reboot is just bootloops with a blank (blacklit) screen and restarts after a few seconds.

I can reach the bios and bootmenu by using the hardware buttons on the side of the tablet (not by means of the attached keyboard). But sadly I can't move/select anything after that. Not with the hardware buttons, touch and/or attached usb mouse+keyboard.

I even tried multiple usb-docks including a Dell WD15 dock.

I also made several USB pendrives to boot from; Fat32 formatted + bios file, Dell Recovery and a Windows installer.

In de bootmenu I can see the option to flash bios and I can see the attached USB UEFI pendrive, but I can't navigate to it.

I can use control+alt+delete with the attached keyboard to restart the tablet. So it's partially working.

The tablet has no cmos battery, but I tried removing the battery for at least one day + holding the power button for 2 minutes to leak away static electricity. But that didn't work.

Maybe someone experienced something similar?

Thanks for your help in advance.