CompuServe Messages

I'm having a strange problem with my Amiga. First, let me describe my system: I'm using an A2000, three drives (two internal, one external–all 3.5" disks), flicker fixer, Sony multisync, modem (serial), printer (parallel), 2 Megs extra RAM, and the 1 Meg Fatter Agnus Chip. If I use a file system such as MessyDOS, my computer freezes up if I attempt any writing to the disk. However, this only occurs if I have installed MessyDOS on my internal drives. My external drive runs MSH fine. I also have had some disk problems using an Atari emulator. (Again, using the internal drives.) I've tried cleaning the drives, but the problem still persists. I believe that there may be something wrong with the chip that handles the internal drives. Could anyone direct me to a software packag (preferably PD), which I could use to test my Amiga's chips? Or would anyone care to suggest what the problem could be? Another quirk that has come up is with VirusX. When I run it, it tells me the ColdCapture Vector is not set to zero. Would my flicker fixer be using this vector? What exactly does this vector do? Thanks, in advance, for the replies.