PT sessions sometimes play back at slow speed

[moogsy]

Recently, many session files are playing back too slow, at wrong pitch. I checked the clocks on all gear (USD, 888/24, Aardvark Aardsync and PT sessions)- all are set the same- to 44.1 The first time this problem occurred was after burning a CD to a Plextor 8/20. I checked the Masterlist file after listening to the CD which was burned at wrong speed, and it played correctly. A couple of hours later, the Masterlist file and the Pro Tools session were also playing at the same incorrect speed, without even using the studio in the interim! I used Norton Disk Doctor on a whim, and it fixed many bad files on two of the four Kingston drives in a Glyph Trip (Catalog Tree, volume and directory problems) and the same session played at the correct speed once again. A couple of days later, the pitch/speed problem recurred in the same session, as well as some other sessions. This time, Disk Doctor fixed some major errors, but the pitch/speed did not get corrected. What is going on here? This is getting desperate! As another point of reference, the computer ( G4 500 w/768 of RAM ) sometimes does not start up properly, and has to be restarted, and today, one of the drives did not mount.