Few things you can try:
1. Reinstall video drivers ( follow my procedure again ). Make sure to uninstall current drivers.
2. Change Power setttings (Got to control panel. There should be something about power there etc)
3. Try this app ( do not know if Windows 7 is supported ) Slick Solutions - MCE Standby Tool (MST)
I do not have a definite solution to this problem as I did not experience it.
As to power settings there is "Power Saver" option as opposed to "Balanced". You can try to switch it and see if there is any difference.