Problem solved. I replaced the current wallet.dat file by one week old wallet backup.
Now there is no existance of my first transaction in the list, I got my unsent balance again.
But not sure why this transaction was not broadcasted. So don't forget to keep your wallet
backup regularly.
Thanks
By the way, in case something like this happen again, you can rebroadcast your transaction to the network easily by the following steps.
1. Go to help -> debug window -> console
2. Enter getrawtransaction ee571cb95553992dc28ac5bd18a566e91899727337c95949cd225fdc93b2680f (Your Tx ID)
3. Copy the output
4. Enter sendrawtransaction <output in step 3>