machine jumps to different position while cutting.

I was cutting a big part from 16 ga. mild steel and had some room left on the sheet after finished and pulled up a couple wall art files for the wife. Started to cut and halfway thru noticed that the machine was cutting the text at a total different spot than it should have. I thought maybe that when the air compressor came on it sent a power surge and the machine skipped data. I turned the compressor off since it had plenty of pressure to get thru the cut. It did the same again. I tried opening another file and it did the same thing. I noticed that when it shifted over to the off data cut it looked like the gantry jumped . I ran it back and forth manually and no restrictions. any ideas?