I have an Asus a55v laptop running Windows 7. I tried to open the BIOS and ended up disabling the XHCI Pre-Boot Mode. After that I saved the changes and my screen just went blank. Is it possible to undo this change in the BIOS settings or repair it?
Windows – Screen went blank after disabling XHCI Pre-Boot Mode in the BIOS
bioswindows 7
Related Solutions
Based on the general symptom of USB devices not working when XHCI is enabled, and working when XHCI is disabled, it would sound like your OS has USB 2.0 drivers but not USB 3.0 drivers.
What does this sort of BIOS setting do? I found a good summary of the choices for a similar 'XHCI Mode' BIOS setting in a post by tonymac user a6f691ac:
XHCI Mode = Disabled - The on-board USB 3.0 port function like a 2.0 port
XHCI Mode = Enabled - The on-board USB 3.0 port function like a 3.0 port
XHCI Mode = Auto - The on-board USB 3.0 port function like a 2.0 port before OS USB 3.0 driver load. If you reboot the OS, the on-board USB 3.0 port again function like a 2.0 port during this reboot BIOS phase before OS USB 3.0 driver load.
XHCI Mode = Smart Auto - The on-board USB 3.0 port function like a 2.0 port before OS USB 3.0 driver load. If you reboot the OS, during this reboot BIOS phase, BIOS is "Smart" enough to avoid downgrade the USB 3.0 port back to 2.0 functionality before OS USB 3.0 driver load. So Smart Auto is faster than Auto on 2nd boot onward, but Enabled is fastest once you are sure the OS has the USB 3.0 driver installed, because it avoid the switching. Making the on-board USB 3.0 port function like a 2.0 port is mainly to support OS installation or to support OS that does not have build-in USB 3.0 driver, so that the USB keyboard would still work if the user plug-in a USB keyboard or any other USB devices into the USB 3.0 ports before the OS is installed with the USB 3.0 driver come with the motherboard.
Background:
Each major version of USB has used a new software interface on the USB controller (1.x: UHCI/OHCI, 2.x: EHCI: 3.x: XHCI), each incompatible with the drivers for the previous version. Newer USB controllers work fine with older USB peripherals, so there is no reason for a computer to have anything but the latest USB hardware -- provided that it's fully up to date with the necessary drivers.
However, when installing an OS, there's the possibility of a chicken-and-egg problem where you have the drivers in hand but they aren't built into the OS installation, and you don't have a way to complete the OS installation and get the drivers on to the system other than using a disk that you need the drivers for.
To get around this for USB, systems either include dedicated older ports (for instance dedicated USB 2 ports on a system that also has USB 3 ports) or else they put a selection like this one in the BIOS that lets you change ports to use the older interface standard on the computer side, and then once you've got the OS on and the updated USB driver installer copied to the system, you can change back, install the update USB drivers, and now everything is running on the newest faster USB version.
The various "Auto" settings seem like an attempt to provide a BIOS configuration that works at full speed normally without having to change a BIOS setting at install time. This is presumably to save tech support calls from individual owners who are reinstalling their OSes, as well as to suit centrally administered environments where all OS installs are done by remote network boot and something like changing a BIOS setting on an individual machine part way through the setup process would be impractical.
The tower has two display ports. It turns out that only one of them was active in the BIOS menu, but both were active at all other times. Switching the monitor to the other port solved the problem.
Best Answer
Remove the CMOS battery from your laptop for five minutes and reinsert it. The CMOS battery is the same size and shape as a medium to large size silver colored coin. This will reset all the BIOS settings back to their factory defaults and restore the screen back to working normally.
ASUS A55V laptop's CMOS battery
If that doesn't work unhook the laptop's graphics card and try hooking the video cable into your TV. Undo the disabling the XHCI Pre-Boot Mode. Power the computer off, hook the graphics card back up, and switch back and connect the video cable to it. Also plug the other end of the video cable back into the laptop's screen.