windows activated with a stolen key can remain activated for up to 90 days, then the activation is checked again an the key inactivated and checked weekley after that. It the activation is ok, the system waits 90 days to check again.
if you update, from windows 8.0 to 8.1 or run the system file checker with the dism.exe the system will remove the hack and then next activation check will fail and you start a countdown to limited access.
very common for people to build machines with the pirate versions and sell them, the machine will work well until you update the operating system.
Some of the hacked versions even prevent any windows updates from being installed. (it just looks like they work but they get blocked)
Sometimes it can be a mistake, you can call microsoft give them your key and they will check to see how many times it has been used. If it has been used hundreds of times you have to buy one. if it is just a error and your key is ok, they may just help you get activated correctly.
(some people get a valid key then run hack software anyway, the hack is detected and the valid key gets blocked on the assumption it is bogus)
most likely you got a hacked version installed on a desktop machine. A laptop might just have a oem version.