Well, my problem is that, when I start Dwarf Fortress, instead of appearing the introductory video and the menu, etc., the window is absolutely blank. I can hear sounds and select the menu options (somehow), but I can't see anything.
Yesterday the game worked well, and the day before, and so on, but I don't know why not today. I didn't change anything and I didn't do anything. I'm using Arch Linux 64-bit.
Have you Installed any new software/Hardware since Before it stopped working, especially Software relating to DF?
No, I just updated my system. Even I uninstalled and reinstalled Dwarf Fortress three times, and nothing.
The bold statements are contradictory; if you've updated your system, that most certainly is changing all sorts of things. I'm not a DF on Linux expert, but if you have indeed updated your system, some of the most common issues to look out for:
* 32-bit drivers. Many 64-bit Linux distributions don't install a full set of 32-bit libraries, which DF needs to run. Depending on version, automatic dependency checkers may not correctly find them either.
* OpenGL graphics drivers. Some distributions have gotten pickier about not including manufacturer-specific drivers; you may need to load them manually, or even specially allow "non free" versions and then load manually. Given your symptoms, this seems particularly likely.
* Rendering to the wrong window and other X weirdness. Do you have, or have you had recently, multiple monitors, remote desktop connections, a projector, or any other situation where DF might be trying to render to the wrong window/device/location?
* DF print modes. Try using different print modes in DF; it could be that you had a required change in DF settings that got overwritten, or system changes have changed what you need. Console mode under Linux *may* bypass certain things and get you a display when others don't work, which is at least a starting point for further troubleshooting. In any case letting us know what mode you are running DF in is probably necessary for any more detailed troubleshooting.