strange Problem with Monitor on RH 9

[othma El Moulat]

thanks Mark for your interest ...
I will proceed by elimination through the steps you specified in your reply...
1.i's not a matter of electromagnetic interference...i don't have any 
electronic device near my Machine...
2.Yes my windoz box is running fine i don't have this problem if i boot into 
my windoz box...
3.what are the parameters that i should verify in the bios ?
6.here is what i got when i run startx:

Fatal server error:
Server is already active for display 0
        If this server is no longer running, remove /tmp/.X0-lock
        and start again.
 
 
When reporting a problem related to a server crash, please send
the full server output, not just the last messages.
Please report problems to xfree86 at xfree86.org.
 
7. my system was working fine when i first installed it...this problem started 
only when my Machine shut down strangely without any body touches it !