Whenever I try to load dosbox at full screen dosbox crashes. I've tried different settings but it doesn't seem to help.

A box appears with the text "SDL_app" in the heading, and then dosbox crashes and quits.

I don't know if this is related to having upgraded my graphic drivers recently or not.

Additional information can be found in the image, from the debugging screen, shortly before it closes down.

Likely this. Full screen works fine for me on Win 7 with other dosbox games.

Ya it was working fine for me a couple of weeks ago, when I last played a dos game. I just recently upgraded to new intel drivers, and new NVidia drivers. I can't figure out why its messing up.

Have you already tried the different graphic modes, especially opengl?

I believe I've tried them all, but I'll attempt to again.

I don't think it's a DirectX version problem, but just to be on the save side it doesn't hurt to install DirectX 9:
http://www.microsoft.com/en-us/download/details.aspx?id=8109

Also try running the game as Administrator and with Compatibility Mode for Windows XP SP3 (if you're using Windows 7) and see if it makes a difference.

And there's another thing, to take effect, it might be neccessary to run the Graphic Mode Setup as Administrator as well. Otherwise it could be, that your changes aren't saved.

To which QFG are you referring by the way and on which operating system?

Well, OpenGl option works.

Whatever is affecting it, is only affecting directx options. I may have to try attempt reinstalling DirectX again.

Nice, according to your error message, I reckoned that opengl would work. Yes, try installing DirectX again (the link is above). On the other hand, if it works, there's no need to waste much time on this, because OpenGL is fine as well.

Well, I'd like to know what's causing it, incase something else doesn't work because of a similar or closely related issue.

Like maybe the directx affecting the QFG5 from loading as well?

It could be the graphics driver. To check, you have to fall back to an older version. But that means fetching some legacy drivers, un-installing the current one and installing the old version. A lot of work for a potential problem, that can easily be avoided by using OpenGL (or will be fixed with the next driver update).
Anyway, try re-installing DirectX 9 first.

Well attempting to reinstall DX9 is only giving me "you are up to date" comment.

So if there is a problem DX9 installer isn't detecting it.

Ahh well I may attempt to reinstall some graphic drivers later. It's no big deal yet. I just hope my problem with QFG5 is not a directx issue as well. No way to set that game to OpenGL as far as I know?

Definitely something screwy with directx tried another game from DX9 era or before (shadowman) and getting similar "invalid pixel format" error;

You could also try using the newest version of Simple DirectMedia Layer, instead of the version that comes with the GOG installer (SDL 1.2.13).

Replace \Quest for Glory Pack\DOSBOX\SDL.dll with the new version (make a backup of the file).

A newer version is here:
http://www.libsdl.org/download-1.2.php
Try Win32 SDL-1.2.15-win32.zip

Looks like the problem was related to video drivers. I uninstalled NVidia drivers, and reinstalled. There might have been some conflicting files, or remnants of older installs. I made sure they were all cleand out.

Things are appearing to work again.

That's good news, so it was the driver - the usual suspect ;-)

Unfortunately not such good news... Looks like the problem has returned after a reboot...

I did find this and it may be related;

https://forums.geforce.com/default/topic/634170/directx-not-available-after-reboot-nvidia-driver-issue-on-gtx580-500-series-/

Guess I'll need to roll back my drivers...