Game locking up then unfreezing.

[Hoyanaqwapaq]

I have played Civ/BTS for about 2 years now, and I am just recently having this problem. I have run the game with no issue on this computer now for about 10 months, and randomly now, it will lock up, freeze, then about 90 seconds later, unfreeze and continue playing. It is very random, sometimes it will do it once, then not again for 45 mins. Sometimes it won't happen for an hour, but then will happen once every 5 minutes for an hour. I have undated drivers, I have cleaned off disc space, I have cleaned up the folders, I really don't know what is going on. I don't think it's a computer issue because it worked fine on this computer for a long time with no issues, even in games where I am play 2 to 3 hours straight.