Okay guys, I fixed it. Despite of the fact, that I tried everything, I set the jumpers on maintenence mode and I was able to enter the BIOS again... This is ridiculous
Legacy boot was disabled, I'm wondering why disabling legacy boot avoids the board to detect my graphics card (probably a bug) and why legacy boot was still disabled although I have done a CMOS reset.
You can't disable Legacy Boot because you have a Legacy graphics. If you want to turn off Legacy Boot you must either use IGP or have a nVidia 600 series card flashed with UEFI bios.
And also, you did not have to use the jumper on motherboard, you can hold down power button for 3-4 seconds and release to get into UEFI settings.