No Logon screen at startup

I’m working with XP Professional sp3, (in a domain with Win2003 server). This morning, at startup, I got no logon screen. The computer first seems to start up normally (Windows XP screen) but when de logon sceen should appear, I only got a blue screen and the mouse pointer, nothing else. When I start up in safe mode, I got a black screen with only safe mode in the 4 corners, also no possibility to logon or to continue. Can somebody help me?