ATI
drivers require that you have Microsoft .NET 4 I think in order to install and use the ATI
drivers.
Windows 7 will install these if you run Windows Update. Have you installed all the Windows 7 updates since the fresh Windows 7 install was done?
Other ideas.
What motherboard do you have in your pc?
Have you installed the chipset
drivers?
Normally Windows 7 picks up and installs the chipset
driver unless the MB is to old or to new in which case Windows 7 may not install the chipset
driver or may install the incorrect
driver. Verify the chipset driver for your system and install it first, then install your graphic card driver if all updates have already been installed.