Weird Issue: A Ding Sound & Game Freezes Up

Sorry if this has been asked before, but I could not locate a thread with my issue.

Issue: This started this week. I will be playing the game (Civilization V: Complete Edition) for over a hour. Then I will hear a ding sound coming from my computer. After the ding sound, the game will freeze up, and I can not shut it down. I have to turn the computer off to exit the game. The issue only has happened twice this week.

Could it be related to overheating?

I have the same issues dont thinx its overheating because 3 august i played civ 5 for about a whole day withouth stopping

my situation:

i verified game cache because i used mods.. on 4 august.. but after that i couldnt start civ 5 because steam servers where to bussy :
http://forums.civfanatics.com/showthread.php?t=572001

The problem solved it selve and i could reinstall civ 5 again. However i now face serious crashes like you after a hour of playing it suddenly crashes. I did anything like reinstalling, checking agme cache nothing works

Anybody have a solution? Now i cant play the game for 30 minutes pretty annoying