It seems that the operating system is not loading the driver even though it has been already installed.
Have you tried updating the system BIOS on that system?
Have you tried with the video drivers provided directly by Gigabyte?
Have you tested manually launching the video driver services? For this just double click on igfxpers, igfxtray and igfxsrvc
Additionally you can try an operating system repair or restore.
Further than this, you may need to test a fresh operating system installation, possibly using another hard drive or partition, just to check that this is not a hardware related issue.
BIOS was irrelevant as it had been working in the past with no issue, but it is the latest version.
The board is generic, you should know that its your chipset. Gigabyte driver is an intel driver, just the one they packaged at release, it is 9 months old. It tried 4 versions including that one.
Manually launching does nothing.
I have now resolved this, I did a system "upgrade repair" rather than a normal repair. This creates a new windows installation and copies all files and programs across whilst fixing any system file issues. This also gives you the option of rolling back to your prior installation.
I was putting off doing this in the hope some bright spark would have an idea I had missed. While I have no idea about intels software, microsoft is something (Ex I.T. Pro) I know a lot about.
Fortunately I didn't get any major problems fixing the OS, which I think was the core problem here, something was seriously borked when I removed the 7970 and installed the intel drivers again. Not blaming you intel, it is most likely .NET or something else Microsoft related (Borked registry settings even)...
If you have OS issues like this in Win7 it is always an option to do what I did when repair fails to fix, rather than reinstalling.
Just run your Setup disk or mount the ISO *in windows not at boot* and run setup, and run the process as an *upgrade* which is the alt way of creating a fresh installation and repairing together with F.A.S.T.