Windows 7 Loading and Freezing Problem

Hello all, my family recently purchased a wondows 7 64 bit computer. It worked fine until a couple nights ago when it started to infinately freeze. It still works perfectly fine in all versions of safe mode but when it loads normally it runs fine for about thirty seconds than freezes on whatever you are doing. I have started up control panel and it didn;'t seem any hindering programs or services were running. The mouse still moves and it doesn't go onto any error screens. The antivirus (Norton) has been acting totally quiet and no suspicious websites have been visited or suspicios downloads been initiated. Everything I have downloaded recently, documents, pictures, has been transferred to an external hard drive. It is extremly nesscary that this computer works, so thanks in advance for all your help.