Systemworks is running a schedule and won't stop

I've been having trouble with a previously very solid machine.  For some reason it stopped booting properly - The Windows XP Pro window comes up then seems to quit.  Then the monitor indicates that there is no signal.  

 

I booted it in Safe mode and scheduled Sytemworks to run Windows Doctor.  It has run Ckdisk  (several times) and it just stops.  When I try to boot the computer it just runs it again.  It now will not boot in Safe mode.  First, how do I stop it from running Ckdisk.  Is Systemworks contributing to my problem?  Any other suggestions?

 

This machine never receives email so I have not worried about viruses, etc.  There have been no programs added since SP3 was put in about 2 years ago.