And you are certain you have downloaded the right drivers (for Win7 64bit not 32bit)?
What I´d test in your case is this;
Download a fresh copy of the latest drivers from your GFX card vendors website or AMDs website if they have none.
Uninstall the drivers you´ve installed from control panel.
Remove the device using Device Manager (you sound like this should make sense, if it doesn´t then let me know and I´ll go into further detail).
Downlad the driver sweeper from
http://www.guru3d.com/category/driversweeper/
Reboot to safemode with network and run the driversweeper
Reboot to normal mode and install the driver you downloaded earlier.
If this doesn´t fix it, you are prob better off reinstalling Windows than troubleshooting any further, it´s like looking for a needle in the haystack, or buying a new GFX card. Preferrably a Nvidia card as you most likely won´t have any issues with conflicting drivers.
A couple of months back the GTX 560Ti was the best bang for the buck card you could get, might have changed lately due to the introduction of Nvidias new series of cards but I honestly don´t know.
Personally I swore to not ever buying another ATI/AMD GFX card after having my 5770 due to issues I ran into with that card and previous ATI cards I´ve owned. This is a highly personal preference though as friends of mine who work with building PCs are sticking by ATI/AMD cards because they think they offer better performance per "dollar" than Nvidia cards. I just happen to feel otherwise based on personal experience