Hi Irene,
One reason I can think of for muffins not rising, is not putting enough batter in the muffin cups.. A rule of thumb is at least 2/3 full.
Also, only grease the bottoms of the cups, if you grease the sides, the batter can't climb up and rise.
Here is a recipe I have used for years.

Raisin Bran Muffins (Make Ahead)
Board: Cooking Club at Recipelink.com
From: Elly, Ohio 7-13-2008
MSG ID: 0083743
MSG URL: http://www.recipelink.com/msgid/0083743