Have you triedStart mining with miner.start()
You can also start and stop CPU mining at runtime using the console. miner.start takes an optional parameter for the number of miner threads.
miner.start(8) true
miner.stop() true
Another way to do the same
When you start up your ethereum node with geth it is not mining by default. To start it in mining mode, you can use geth --fast --cache=1024 --mine --minerthreads=8 --rpc