It sounds like you have an older furnace, most older furnaces don't have a 3 amp fuse. Did you check for power to the furnace? Try to plug something in the outlet to see if it has power. If it has power, then you need to check the transformer for 24v. Try to reset the roll out switches. A roll out switch should have a button for you to reset. Here is a picture of the roll out switch
http://www.appliancezone.com/ShowProduct.aspx?ID=6776
if you press the roll-out switch and the furnace turns on, then you might have overheating problems.
http://www.appliancezone.com/ShowProduct.aspx?ID=6776
if you press the roll-out switch and the furnace turns on, then you might have overheating problems.