When starting Risk you are spread out and a few bad turns of the dice can leave you so thin you have nothing to attack with. There is nothing in the rules about this. Am I to assume you have lost at that point?
Most certainly not!
You will still receive armies and be able to attack in a future turn, as the rules make clear (see page 6: Getting and Placing New Armies - Territories) that every player with at least one territory receives at least three armies each turn for territories, even if owning fewer than 9 territories.
In order to not be a target of other players while you are weak, it is best to hold as few cards as possible, ideally zero, until you are strong enough to have a chance at defending your self, so don't attack at all.
It's all a matter of diplomacy. In the situation you described, you are "down but not out." (The exception would be a two player game, which you lost, because your one opponent has "everything else.")
If there are multiple players, they would all do well not to attack you (for the time being), and concentrate on each other. If you receive the minimum of three armies per turn, you might not want to attack either, until you've had a chance to build back up.
What you need is a situation where there there is no player that is stronger than the sum of all the other players including you. In a three way game, that might be hard, because one player might get far enough ahead of the other player that you can't make up the difference. But the more players there are, the better chance you have to survive (or at least go down fighting), using diplomacy to maintain the balance of power, to the best of your ability.