Isn’t there a legend somewhere on the screen (generally at the bottom), that tells you the options you have? Generally, to exit form a BIOS screen you hit F10 to Save & Exit.
I have an ASUS netbook myself, possibly the same one as you, that has a similar BIOS interface. There’s a chance that the storage device may have failed or there’s a problem with your Windows installation.
Have you done any big updates recently or attempted to format the disk, install Linux or similar?