UDK Editor perspective viewport weird black veil surrounding the camera in lit mode

[electron]

Hello !

Here is the problem, I'll try to explain it as best as I can, as English is not my mother tongue, I'll use screenshots to help me.
I recently downloaded the July 2013 UDK Beta ( Version : 10907, Changelist : 1715227 ), and installed it without any problems.
I've played the game supplied with it, just to see if everything was OK. Everything went right.
It's with the editor that I have a problem, in particular within the perspective viewport in lit mode.
Before you see the screenshots, I give my system specs :

Operating System	: Windows XP Professional Service Pack 3
Processor	: Intel(R) Xeon(TM) CPU 3.00GHz (4 CPUs)
Memory	: 2046MB RAM
DirectX Version	: DirectX 9.0c (4.09.0000.0904)
Card name	: NVIDIA Quadro FX 3500
Display Memory	: 256.0 MB

I know my computer is a little bit old, and my graphic card is (afaik) not a common one, but I already used UDK ( in 2011 ) without problem.
It should be enough for the moment, as I'm more focused on the gameplay than on the graphics, anyway, here are several screenshots to illustrate the problem,
I don't put them on the forums as they are relatively big, and I don't wish to overload the page.
The screenshots are stored on my blog, and there's no ad.
When those screenshots were taken, my graphic card's drivers were up to date, I tested with an older one and it didn't change anything, maybe I should keep trying
with other ones ?

1) in unlit mode	: link( everything is normal )
2) in lit mode	: link( notice how it's black )
3) in lit mode	: link( as I zoom out the black veil disappears )
4) in unlit mode	: link( this one is taken while doing the "Creating levels" tutorial )
5) in lit mode	: link( as I add a point light the editor switch in lit mode, it's black again, even when I build the lights )
6) in lit mode	: link( I've dragged the light up and built the lights )
7) in lit mode	: link( again as I zoom out the black veil surrounding the camera disappears )
8) in lit mode	: link( in orthographic top view, the surface is normally lighted )
9) in lit mode	: link( I played the level and moved the camera while taking the screenshot )
10)in lit mode	: link( the "SimpleCourtyard" map )
11)in unlit mode	: link( the "SimpleCourtyard" map, again )
12)in lit mode	: link( the "ExampleMap" map )
13)in unlit mode	: link( the "ExampleMap" map, again )

If I already used UDK before without have had this problem, what has changed since that could explain this issue ? Do someone know ?
I could download an earlier version, but then I would certainly miss important features ? And if I had to, which one should I try ?
I can still work in unlit mode but I won't be able to test, is there a possibility to test without lighting ?

That's it ! Thank you for reading !