What happens if a new Bid price is substantially lower than the last Close price - close to 20% lower, and Ask is shown as zero? Will trading take place? Is this likely to be "big money" with insider information signalling something is about to happen to the stock?
Depends on when you are seeing these bids & asks-- off hours, many market makers pull their bid & ask prices entirely. In a lightly traded stock there may just be no market except during the regular trading day.