My watch is not G-Shock, but close. It's a Casio EDB-300AD-6VER (has digital + analogue). What happened was I opened the watch to change the battery. At the same time I had an idea to remove some dust from between the glass and the screen. While successfully removing the dust and putting the watch together again, I found out that the arms are now stuck. I'm quite sure it's because I accidentally moved the arms around a bit while wiping the screen. So probably the minute arm moved a few minutes back or forth. Not by force, but it moved really easily just by touching it.

What can I do to get the arms moving again? Should I move the arms back and forth randomly or does that just make it worse?

It's stuck so that the arms don't advance at all, not normally nor by trying to adjust the time. The digital part of the watch works flawlessly.