After playing S2 for a number of months I was supprised to find out my game had reverted back to Demo yesterday. I was able to unlock it again but im not happy because it's used one of my unlocks and why did this even happen in the first place.

The only change my PC's had recently has been the uaual MS patches and the addition of a dual core CPU.

It could be because of your processor update. LFS's unlock system uses a snapshot of your hardware configuration as a way of "identification".
It's no big deal as you receive new unlocks anyway.

Not sure why LFS locked itself again. But you get one new unlock every Friday Morning (up to a maximum of having 2).

Great, thanks guys, I thought i only had a finite number of unlocks before i would have to purchase it again. LFS did run for a week with the new CPU before it locked it self back to demo.

Anyway all sorted now, cheers.

Quote from radweld :

Great, thanks guys, I thought i only had a finite number of unlocks before i would have to purchase it again. LFS did run for a week with the new CPU before it locked it self back to demo.

Anyway all sorted now, cheers.

Usually that, getting locked and then unlocked randomly, is because the PC has been in hibernation/snooze mode before starting LFS. Always make sure that's not the case, especially before unlocking LFS.