Does the same thing happen when playing other full-screen games? If so, you may have a problem that only occurs when DirectX is demanding increased power from your processor and graphics card. Could be an overheating problem (maybe a fan died, or a heatsink came loose) or a power problem (possibly the PSU is dying of old age), or a RAM problem (sometimes RAM errors only show up when you use a machine intensively, and RAM corruption usually causes a total crash).
If other games (that are at least as graphically demanding as Age Of Empires II) do not cause a crash, then maybe the game just has a wild bug that causes a total crash. In which case, maybe try looking for a patch for the game to fix such bugs, or try newer or older drivers for your graphics card, to see whether that fixes the problem.
Hopefully it's a software problem rather than a hardware problem. Hardware problems require quite a lot of effort and possibly money to fix.