Your account is locked by default due to which you are not able to make the transaction. To make the transaction, you have to first unlock the account. You can unlock the transaction using this command:
personal.unlockAccount(eth.accounts[0], "<password>")
Replace <password> with the passphrase set for that account and then send ethers:
eth.sendTransaction({from:eth.accounts[0], to:eth.accounts[1], value: web3.toWei(4, "ether")})