Need help for bios Update Dell Latitude XT2

[macwig]

Hello,
after updating the BIOS of my Dell Latitude XT2, I have had a blackscreen. After removing the CMOS battery the laptop starts with a blank screen and a blinking cursor in the upper left corner. Then nothing happend any more. I tried to put the newest BIOS (http://downloads.dell.com/FOLDER01556667M/1/XT2_A15.exe) on it, but the instructions (https://www.bios-mods.com/bios-recovery/...-recovery/) does not work. With the phoenix tool I got this massage:
Pubkey in 48_16.ROM (x1)
Marker (2.1) (DELL  M09     ) in 49_17.ROM (x1)
I tried both names with the packed and the unpacked file. None works.
The 1GB USB stick was prepared with WINCRIS.EXE and I've done it step by step as the instruction told.
Have anybody an idea where's my mistake could be?
Kind regards
macwig