[SLE] X Server doesn't start at boot

Hi all I have a Suse 9 Pro installed. When the linux boots X server doesn't start and it seems that Graphic card doesn't supply the correct electicity. I restarted the system and I started with the failsafe option. I logged in as root and giving the command startx or int 5, the Xserver started properly. Do you know what it may cause that failure ? Thanks in advance