I assume that you've tried all this:

1. Wipe out and re-format your HD.
2. Re-install your OS (keep it basic - no bells or whistles). I'd even get another copy of the installer, in case the one that you've got is "krafted".
3. Install ONLY ONE MIDI application and the necessary drivers for your cards. Nothing else.

4. Do all the setups and configurations according to the manuals.

You have to keep things very simple to be able to trace the problem. "Kinda" doing those steps isn't what I'm talking about.

If after doing that you're still haveing problems...
Then you've got a hardware-related problem.
Anything....
Bad RAM, bad I/O bus etc..

ED