Steam freezes my Asus G73j laptop. Help plz

[Goaker]

There was a time when I could start steam in my Asus G73j and play without any problem. Now, it freezes before it even loads. Some times it says it's updating, then freezes the laptop and I have to reboot. My desktop hasen't given me any problems even after multiple reinstalls. System drviers are up to date, Win7 home, ATI mobil 5870, 8G ram, momentus xt 500G drive. Any one having the same problem?