MultyPlayer doesnt start ,

Hi guys , i have windows xp 32 bits sp 3 . all drivers updated ..so i installed Call Of Duty 4 Modern Warfare ...i layed just multyplayer for a while ..it works good like 45 fps
Im not lagging or something..but when i started the next day its just pops up a windows with a Call Of Duty 4 logo then a black screen appears for 1 second ..then i dissapers ..sorry for my english . HELP PLEASE !