Can't access BIOS

Hi, I've got a XPS 13. Today I accessed BIOS to disable Secure Boot and Intel Rapid Start (I'm trying to install Ubuntu with UEFI), this was fine. Then I logged into Win 8 and restarted holding shift in order to access boot menu and the pc freezed. Each time I try to access BIOS from windows it freezes (i can't do anything and I have to use power button to shutdown). I can't access at startup even if I press F2 a lot of times. Finally I tried to flash BIOS but the pc freezed while it was reading the BIOS.

The pc works fine, windows start without problems. How can I solve this issue?

Thanks