Time and density sounds like the problem. Don't know how many cookies (density) you're trying to heat for how long (time).
Try this .... dampen two paper towls .... just get them wet under the faucet and squeeze them out ... then place one on the bottom, your cookies on top of that, then lay the other one on top of the cookies. Then, "nuke" them for 15-30 seconds ... and allow them to sit for about a minute before you open the door. They should come out warm and moist.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain