The PSU ought to be fine in that situation- the 5750 uses VERY little power- generally doesn't pull more than 75 W at load unless you crank up furmark. What version of the ATI Drivers are you using? Also- does it crash in a specific game or in all the games you try to play? Did you upgrade from another ATI card, or from an Nvidia one? If you had an Nvidia card previously, then you probably need to uninstall all of your display drivers, reboot into safe mode and run driversweeper, then reboot and reinstall the latest ATI drivers.