thank you tayvano
answers are
Have you ever done anything with your RPC?
Yes geth node runs on this pc but geth was shut down before launching mist that I usually do
Have you ever messed with other settings in geth or another client?
No I don't think I changed settings and another client aa well
Have you ever pasted code from a website or forum or whatever into your command line?
the following link's code has been put it contract in order to get DAO in mist
https://raw.githubusercontent.com/slockit/DAO/master/deploy/interface/minimal.json
Have you ever unlocked your account to allow access for another site?
never
Do you have any remote access / screen sharing programs (ie: TeamViewer)
I have a teamviewer installed but checked 'Connections_incoming.txt' which in '/var/log/teamviewer11' directory only shows connections that I made in march when I installed it earlier.
Do you have a firewall set up?
UFW is enabled and only allows 30303
What do you use to mine? Is that the same node that holds this account?
Yes it's same PC
Is there any possibility your private key was compromised?
I don't think it's backup is on cold usb storage and never touched it.