This is an odd problem that I can't find any mention of -let alone a solution for.

As the screenshots show; all menus, loading screens, inventory and HUD are running within a different sized space than the game itself.
http://imgur.com/a/hiDly
The pointer, however, can move across the whole screen - which leads to some annoying mis-positioning of the pointer, as you can see on the inventory screenshot (the item hilighted is not near the pointer...)

The main menu map is still behind the loading screen in the first, the HUD is in the wrong place in the second and the inventory screenshot shows the problem with the mouse pointer positioning.
Oddly, if I play with Darnified UI installed, the settings menu allow me to move the HUD outside of this smaller area it loads in. This does nothing about the pointer mis-positioning problem though.

This happens even if I change the game resolution. Whether at 1680x1050 or down to 800x600 the menus load within a different sized area.

I have not installed any new mods before this problem occured. It occured after a crash-on-exit (common occurence...) and started the next time I loaded.

I have tried reverting to the vanilla Oblivion data as detailed here:
http://wiki.tesnexus.com/index.php/Revert_to_vanilla_data
But after doing this and loading from just the Oblivion master esm and nothing else, I still get the problem.

Given the problem remains when following the above instructions, I assume it's not a problem with any of the XML files.
Which leaves me at a loss as to where to look for the source of this problem.

Any ideas how to fix this would be really appreciated. Else any ideas as to where to start looking for the cause would be welcome too.