For several years now I show a countdown on this website (move your eyes towards your right and you will see it). It counts down until the Death of Computers.
'What does it mean?' you might ask... Here's the solution/explanation:

Countdown until Death of Computers

I would like to refer to the day Skynet becomes aware of its capacities and blows us humans away.. but it ain't the case with my countdown.

Actually the timer is counting down to January 19 2038, 03:14:07 UTC. What basically happens then is that the unix timestamp, which counts the seconds since January 1 1970 reaches the maximum, the highest possible number.
In 32bit systems this means that the system time will look like this:
11111111 11111111 11111111 11111111
32 single bits having the number 1. As I'm sure you know, computers "speak" binary: 0 and 1.

Once all 32 bit are having the number 1, the maximum number is achieved and it will logically continue like this:
10000000 00000000 00000000 00000000

But this messes the time system completely up! The human date will show 1901 and the unix timestamp will show something like -2147483643. Now try to program something, e.g. with PHP which uses the time() function and therefore the unix timestamp -> which is now a negative number!
Applications, Operating Systems and maybe even the hardware (depending on firmwares etc) will fail. This will have a global effect as so many things are connected now.
This problem is also known as Year 2038 problem, you may find more information on Wikipedia. I accidently stumbled over it after a typo of a time variable in a self-made PHP program what made me aware of this.

But of course I'm exhausting this fact a bit. Since this problem only affects 32bit systems, the problem is of course not known in 64bit systems, as there are 64 bits of 0 and 1. With 64bit this problem will only arrive in about 292 billion years. I don't think that mankind or earth will exist that long to worry about such a problem...