I have a Platinum 755Q.
If you are getting loops on top, you may be threading the machine incorrectly. The presser foot must be in the up position, when threading. If not, the thread will not be seated correctly between the tension disks.
When filling your bobbins, be sure the raised logo on the plastic bobbin is facing upwards. You are using Viking plastic bobbins, right? The logo should be facing upwards when filling the bobbin and when inserting the bobbin into the bobbin case under the top cover. You should also feel a click, when the thread is properly threaded in the bobbin case.