[Probem] Black Screen / Resolution change MS v112

Hello!
I'm making this topic be cause I have some problem with playing MapleStory in one of my GF's computer.
I execute the game from the webpage and the launcher, It goes well with the gameguard/BlackCipher, but then It's change the resolution of the screen to 800x600 and it's stays like that.
Hardware and Software information:
OS: Windows XP SP3 32Bits
CPU: Intel Core 2 Duo E7300 2.66 Ghz
RAM: 4 Gbs DDR2
Video Card: GeForce 9500 GT.
DX: 9.0C

I don't know what to do now.
I hope I can find the solution.

You mean when you start it up it's at 800x600? I think it's because the login server only has that one resolution. Not sure if the other is available on the login server. It should go back to 1024x768 when you enter a game.

I recommend using windowed mode on either of the two resolution settings in the game unless your monitor's vertical pixel height is max 768 pixels or fewer.

Finally I came with the issue.
It's the Direct X, It's the last version but it's corrupted (I give the clue with trying to play with Project 64).
I googled about how to uninstall it, but It talks about reinstalling the O.S u_u.