Why am I only getting 2/5 the Satellite recteption that I usually do?

My Tom Tom usually gets about 10 satellites. However, now it's only getting 4. With only 4 satellites, the unit is basically no good. Is there a problem with my unit or is there a problem with the satellites? Do I need to do something to correct the problem or will it correct itself or do I need to go out and buy another brand to get a product that is reliable?