I have a Maytag Neptune Model MDG4000BWW, SN#17084094WM that suddenly stopped heating. I have tested the safety fuse & it's OK. I replaced both gas valve coils, but it still doesn't heat. Where do I go from here?

Try troubleshooting it with a meter. Never ever change parts without checking them first. It never works, anyway. It's probably dirty and needs cleaning and the replacement of a safety fuse. All safeties are wired in series so with a meter set to "ohms" you will have no problem finding the blown safety. You will have to totally take it apart and wash out each part to fix it right. That means to clean the door, all air ducts, and the blower wheel and housing. Here are some manuals: https://dl.dropboxusercontent.com/u/8010163/Maytag%20Dryers.zip
https://dl.dropboxusercontent.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf