Random coin placement

[i_need_help]

i only want one coin on my screen at a time, but once i pick it up i need another coin to appear in a random place on the screen. Can anybody tell me how to modify my code to do this?

this is my code:

onClipEvent (load) {
this.stop();
}
onClipEvent (enterFrame) {
if (this.hitTest(_root.car)) {
this.gotoAndStop(2);
_root.score +=1;
}
}