Neither my heat or air conditioning will cut on- what could be the problem I can't even get the fan to come on?

Check all electrical breakers, and any fuses that are on or near the furnace. Sounds like a power problem. Check for power to unit, if none found, trace back to the problem. Good luck and please let us know what you find.
PS. Many times there is an ssu swith located on the side of the furnace or near the furnace. The switch box will have a cover that flips open to reveal a fuse.