Problem with codecs on Latitude D520?

Hi,
I bought a new Dell Latitude D520 with Windows XP Professional (SP2 included). While the videos played, everything is all right. But when I close a player (WM Player 11, or Media Player Classic), screen begin to flash. First time I`ve thought, that problem is occured by installed codecs (at first i had a K-Lite Codecs), so I`ve install a newer version of K-Lite. Everything was the same. Today I`ve used to ffdshow, and nothing. It is the same. Im desperate.
I have a latest drivers of chipset, graphics,...
Notebook configuration: Core Duo, 15" XGA, 2GB RAM (533) - one 1GB modul added, Intel 945 Graphics shared to 244MB, 60GB HDD Samsung.

Please help me..
Thank you for your answers...

 

What videos? WMP doesn't play DVDs by default. You can use VideoLAN which is free and works quite well.

 

I don`t have a problem only with DVDs. I have a problems with all other video formats too - .avi,.xvid,.mpeg,.....
I`ll try to install that VideoLAN Player, but it doesn`t deal with my problems.
THX