When installing new drivers be sure to follow this procedure...
1# Restart computer and boot into safe mode (press F8 shortly after the computer 'posts').
2# Remove the current ATI drivers via the control panel > add/remove programs menu.
3# Restart.
4# Run driver cleaner filtering for ATI catalsyt drivers.
5# Install 4.12 drivers.
6# Restart.
7# Job done.
Links:
4.12 cats
Driver cleaner
This is assuming you are using an ATI card btw.