I own a Viking and have managed two dealerships.
The 'obvious' one is like everyone said, is the needle with the flat side to the back and inserted all the way up.
You did not state if you had a mechanical or computerized one. If it is mechanical, check to make sure your stitch width is on ZERO. On some of the mechanicals you can slide the width back and forth, on otheres there are three needle positions. If that is the case make sure you are in center needle position.
As to the other machine having bobbin issues. Is the thread in the tension guide of the bobbin? If not you will get a mess. By the same token if you do not thread your upper thread with the foot raised the thread will not go in between the tension disc up top and that can cause a mess.
Feel free to PM me is you like. :)
Peggy