When you opened the bag, were the melts clean looking, or did they have some white blooming on them? Old candy melts will not melt after a certain point on the shelf.
What wattage is your microwave? If it's a smaller model, it probably doesn't run on more than 900 watts, so it will take longer than the instructions on the bag read.
But there is hope - since you want to print with the chocolate, there is a chance that you can resurrect it.
You need it really liquid, to make your decorations. There are a couple of things you need to do.
I take it you are using the 12 ounce bag of Wilton melts, correct?
First - if you have a glass bowl or glass measuring cup, put half the melts into it.
Second - add two tablespoons of clear, flavorless cooking oil or vegetable shortening.
Third - microwave for 1 minute. Remove and stir. Microwave another 20-30 seconds. Remove and stir.
If they melt this time, proceed to the next step.
Fourth - stir in the rest of the melts. Allow to sit for 1 minute, then stir again. If the melts need more time, only give it 15 second bursts. The candy dots should only be melted 2/3 of the way when you are done. They will melt the rest of the way while standing.
If you need to thin the chocolate more, just add more oil or shortening. I would only add about 1/2 teaspoon at a time, until it gets to the consistency you need. But honestly, I don't think you're going to need more.
When using melted chocolate for drizzling, stamping, or decorating, you should always thin it with some kind of fat, so it sticks better. If you use straight chocolate for the type of work you are talking about doing, it will fall off when it re-crystallizes.
Now, let me explain why I always use glass to melt chocolate or melts in the microwave. The glass retains heat, and the candy melts via what chefs call "carry-over heat".
You can take a 4 cup glass measuring cup and add an entire pound of melts or chocolate. Then microwave it for 1 minute; take it out and stir. Zap it for another 30 seconds, remove from microwave, and allow to sit for about 2-3 minutes.
Let me know if this helps.