No error message in the event log, but the computer freezes

More than likely it's hardware. More likely than that, overheating. Download RealTemp and report your CPU temps.

Also, what are you doing when the system freezes?
 
Overheating can not be. The computer sometimes does not always freezes when I turn it on after the greeting Windows 7. appears a blank light blue screen
 



Overheating can not be. The computer sometimes, does not always freezes when I turn it on after the greeting Windows 7. appears a blank light blue screen