What caused this in Garageband and Logic?

I use logic 8 and Garageband just to get my ideas down quickly (which works great) when i am inspired and i am having the same problem in both.

My Mac Pro running OSX 10.4.11, 2.66Ghz with 1 Gig of RAM is connected to a M-Audio Keystation 88es(by USB)

When i am using the keyboard and recording or playing Garageband(usually with multiple tracks of VST's) will:

1. drop the connection with the keyboard
2. mess around with the pitch of the sound(as if i was applying a pitch bend to what i was playing) and play the notes at a different pitch!!!
3. Volume controls will jump up and down by themselves.

in Logic it will do the same!!!

Also when i am turning on the computer the screen flashes.

What is causing this? Latency, not enough RAM, sound card problem? How can i fix it?

Anyone know or have ideas? It is driving me up the wall and i have been having to reconnect(turn off and on the keyboard every time to get it to reset. It does the same thing with my M-Audio trigger finger.

Help!