strange Problem with Monitor on RH 9

[othma El Moulat]

Hi guys;
I'm facing a realy strange problem wih my PC's monitor when running RH 9...the 
screen monitor looks fuzzy unstable and keeps waving ...I don't know from 
where this problem came! but what is strange about it is that this problem 
disappeare when i boot on the windows partition box on the same machine! 
Important thing to say: I was absent a while when my RH 9 was running and when 
i came back i found the PC shut down without any body touches it !( STRANGE 
!!) this might be the source of this problem...
I don't know how to proceed to fix this malfunction...please help!

thanks
othman.