Sorry, Martin - I hadn't realized your configuration.
 
Is it possible that your hard drive is set to turn off after some period of time?  It has been 10+ years since I have dealt with any devices going to sleep, but I seem to recall the possiblity the hard drive could turn off, but the rest of the display and PC not actually go into sleep mode?
 
It just seems so consistent with something along those lines that I want to make sure no chance of that is possible on your system.
 
Bob Bone
 

If there is a chance you overlooked something it may be covered here regarding power management for XP http://www.homeandlearn.co.uk/BC//bcs4p5.html

hi Bob
 
the only setting i have is screen-saver after 20min
 
harddrive & all other setting (sleep mode)are all active
 
note to mention(i dont leave my computer i just do some other stuffs.while my SONAR is open
& also i do have multiple projects open,but only the one that have midi-track)SFZ player..
the audios play but not the midi-tracks..
 
all other project (audio only work just fine,,
 
weird

not really my XP is "tweaked" for DAW the only thing i was having was screen-saver wich i disable it
 
thx