The Bernina 730 Record is a great little machine. If the selector levers are sticky/stuck or the handwheel is stiff or does not turn, about 98% of the time the machine needs oil.
Mechanical machines need to be cleaned and oiled regularly just like your car. If the machine sets in storage for a while or is used often but not oiled or cleaned regularly, the oil that exists in the machine will eventually thicken and acts like glue. (Sometimes you can see a dirty-looking dark gold or brownish goop which is usually old oil.) Then your machine is frozen.
First, open the top and bottom of the machine and sweep out any dust, dirt, lint, or stray threads.
Now, oil your machine (there's a diagram below). There are quite a few oil holes (both in the top and bottom of a Bernina mechanical) that require periodic oiling (see your machine Manual). If a metal part is frozen, buy a bottle of liquid Tri-Flow Synthentic Oil (from the hardware store) and put one or two drops in all the spots shown in the manual. (DO NOT oil rubber parts, the two white plastic gears, the belts, or the metal CAMs!!! NEVER use 3-in-1 oil, cooking oil, WD-40, or oil from your grandma's sewing box. And do not put more than one or two drops of oil at a time as over-oiling will also damage your machine.) It also helps to slowly hand rotate the handwheel and, while watching things that move, apply 1-2 drops of oil every place that metal rubs against metal. Do this also with the selectors and dials.
Then, using your hand-held hair dryer, direct hot air into the internal part of the machine (top and bottom). The metal may become hot to the touch. Then try to gently move the handwheel and the selector levers. Repeat. Let it set overnight. Then test again the next day, and repeat the process if needed.
To maintain your machine, a good recommendation is to oil every time the bobbin thread is changed, every 8 hours of constant sewing, or every six months if the machine is not in use. Use a good quality oil, ie Bernina oil for "mechanical" machines. When oiling, also be sure to brush out the dust and lint (especially around the feed dogs and bobbin works).
If the oil in your tube looks dark colored, throw it out and get some new. I've run across some old sewing machine oil in the can that looked like dark honey and stunk to high heaven. Get rid of it!
Treat your machine well and it will serve you well for many years.
This is an oiling diagram of an 830 Record which is very similar to the 730.
This is an oiling diagram for the 930 Record. Also fairly similar.