TURBO CNC "hangs up" (freezes) part 2 "i have a clue now."

well today i decide to give it another try...the machine jogs well (I
still didnt check again the X axis for its measures-difference)
now i can certainly say that the computers, just frezzes a short time
after i turn my spindle "on" and the stepers keep runing, even if it
use the E-switch. (even without using the relay conected to parallel
port)

i use a siemenes micromaster 420, to power a three phase 1hp motor.
the micromaster is AC 220v input, and AC 380x3 output. its conected
to the same powerline that the pc is, but i use an extention to
conect the pc almost 15m far.

so my first guess is : interference. but i dont know...is it high
frec? or low frec "noise" ...in my opinion it should be high, but the
micromaster works as an frec converter, it changes the line frec, not
the voltage, so it keeps the 1hp even at 10 rpm on the motor, or
2500rpm.
i use the motor, just to try at 5hz, 10hz and even 20hz on a 1HP 2400
RPM motor. but the pc still freezes like a minute after i turn it on

so i thinking on getting a line filter..but what type???
THANKS IN ADVANCE
MARCOS