Standard VGA driver is a placeholder driver given by installer when it doesn't have a newer driver (yet). It may be updated via optional Windows Updates so check there first.
If you had better resolution before then you might get it back by following joodoo's idea of rolling back the driver on Driver tab of the installed device in Device Manager.
If not you want the latest driver on the Asus's Support Downloads webpage for your model, as suggested.
As to what might have changed it, the first suspect would be AVG bloatware. No one here recommends AVG since it bloated up a few years back and causes problems. Use Microsoft Security Essentials
or Avast 6 for best performance with the Windows 7 firewall.