Black screen before Dell logo after bad boot settings

Hi.

I've set "uefi ipv4 boot" in first boot sequence on my bios. Since this modification, my computer can't start. I got a black screen before the Dell logo. I've tried to do a bios reset by removing the CMOS battery but nothing changes. I've tried to unplug the HDD, the ram and the CD player but nothing works. When I try to start the computer without ram, it make some bip noises. The BIOS is up to date and I've made a diagnostic from the bios menu one day before the bug, and the diagnostic was OK. Ive tried to press all the functions keys at startup (f1, f2, etc...). I've started to press escape, control, delete, but nothing worked. I've tried to plug a bootable USB key but nothing... Can you help me ?