Question : Problem: Cannot set a higher resolution than 1024x768 any longer

Hi, first time posting a question here so hopefully makes sense.
I am running Windows Vista Ultimate SP1 with an Nvidia GeForce 8600 GTS video card and a Viewsonic VX2245wm monitor.
2 days ago I was mucking around with a game called Supreme Commander and noticed that on the CD it had an option to install DirectX which I proceeded to do. Before this I assume that I was running Direct X 10 (as I understand it comes with Vista) but the CD was actually version 9.0c which I realised after my error.
The problem was that after exiting the game (and I had run it dozens of times before) the display settings maxed out at a resolution of 1024 x 768 with only the option of downgrading this to 800x600. I have reinstalled the monitor driver, reinstalled the video card driver, and reinstalled DirectX 10 all to no avail.
The other problem that i've noticed is that my monitor does not automatically go out of sleep mode again when rebooting my PC but instead I have to turn it off then on again to awaken it.
The only thing I have managed to be able to do is when uninstalling the monitor drivers the display settings give me an option of increasing the resolution beyong 1024x768 BUT whatever I choose I find that the screen goes black and I have to reboot whereupon it goes back to the same problem with capping the maximum resolution to 1024x768.
Please help.

Answer : Problem: Cannot set a higher resolution than 1024x768 any longer

Seems the solution was quite simple in the end. Under the advanced display settings | monitor tab I unselected "Hide modes that this monitor cannot display" this then gave me the option of increasing the resolution. Notsure why it wouldn't display these resolutions with the box ticked but it all seems to be working fine now.