The first time you play a DVD on a computer's DVD drive, the drive needs to "set the region" to whatever the disc is.
For example, to play normal DVD's your drive needs to be region 1. From that point on, all region 1 (and "all regions") discs will play on that computer.
But you CAN change the region number, BUT you can only change it a set number of times before it is permanently "locked" in the drive's firmware itself.
On a PC's DVD drive, I believe you can change the region number FIVE times before it becomes permanent. So if your drive is already set to "1" (that's 1 change already) then you change it to "2" (2 changes now) when you want to watch a regular DVD now it's gotta go back to "1" (3 changes thus far...) and as you can see you can lock up your DVD player rather quick this way. Not adviseable. The region change feature is intended in case you move overseas and things like that, not for playing discs from around the world.
While not a laptop, I have a PC with two DVD drives, and I made sure one of then is set to region 2 and the other is region 1.