I recently replaced my heat sink. Since then, sometimes my home hilt machine will mess up and my OS (Ubuntu 12.10 64 bit) will say that I don't have a graphics card. This also happened when I first built the computer. At that time, the problem went away after about 2-3 days. What is this problem? My CPU is an Intel Core i5 3570K (stock clock) and my hesitant is the CoolerMaster Hyper TX3.