Mac Book Air 13 cpu running almost 100%.

My two-year old Mac Book Air 13 processor is running almost 100% of the time. 86% of it is consumed by the system while the user get less than 6%, and open apps get about 5%. It is extremely slow, too slow to use. The fan is running constantly at full rpm. The desk top is empty (all files moved to documents folder). Trash is empty. iPhoto trash is empty. All apps are off. SSD memory is sufficient. I have attempted many cures, including the SMC reset. Nothing has worked so far. Can you help?