Sue,
You have already proven yourself far and above the 'average female' by 1) getting a tank, and 2) by wanting to fix it yourself!
Welcome to the band of brothers, and now, sisters.

Your symptoms point to no signal to the recvr. Could be grounded, or broken, or disconnected, antenna wire in the tank (as hdbeast suggests). You'll have to carefully open up the tank. It's the black wire, screwed to a brass post on the back of the deck (the top of the hull) that the silver antenna, on the outside sticks onto. Following that wire, it goes to a cheesy silver connector, and from there to the recvr circuit board. Check to make sure solder joints along the way are solidly connected and that the silver connector is connected. Then wrap the connector with electrical tape (that black vynal stuff you find at RadioShack). That should take care of anything you can address inside the tank.

You say that you have tried different chrystals (I assume in the xmitr) and even a different xmitr. That should rule out anything external to the tank (xmitr), assuming that the new chrystal and the chrystal in the new xmitr were the same frequency as the tank recvr. (very low chance that you broke the tank recvr's chystal, unless you dropped the tank. If so, you would have broken much more than the recvr xtal.

good luck,
Splat