Dear Ding Zhou, Thanks for your inquiries about my probleme(s). Well, I am now with 14.04 (I was 13.04) but only after a few long days and short nights. I really had "THE Super Mess", stiil blocked with no update/upgrade....... A friend said "stop this, back-up your data and we will re-install together" A clever chemist, believe me. We did try to install 14.04 ( a dvd made by me and tested and working perfect) no succes, then 13.10 (an other dvd made by me) and here start the "fifth dimension" As 13.10 was ok (live session) I did install Unetbootin and made a Net install USB Key,(which is stupid when Unetbootin is installed on the PC you want to re-install) checking MDS5 and stuff like that, so this USB Key start the job for Ubuntu 14.04, take times but all looks fine, and when reboot TUT....black......and login with a terminal tty.....pswd (never OK the first time, a real mistery) start Ubuntu 14.04..........and nothing, spinning round as no connection available even iff that connection was installing 14.04 a few seconds before rebooting. My friend was very ennoyed and I didn't said anythinks.Due to the fact that he must be at work at 06:00 am he left me alone at 01:00 am with this situation. So, impossible to start X but looking by the terminal (cd - ps - cwd...you know better than i) ALL WAS THERE (14.04 in the system ????may be incompleted but how to know?). At this point re-istall with Kubuntu to test (still the USB Key for Net install) lead to the same mess.....re-istall ubuntu 14.04......no connection after reboot and always starting Ubuntu 14.04 (smaller letters than usual, strange too) before the black screen ....but able too re-install as much time as I want. And no way to use a DVD too, blocked by my onw install which was out off order. Even when installing other Dist than Ubuntu, it always reboot in Ubuntu 14.04 (not working and trowning my PC from the world) At the end, I used Aptitude in terminal session to erase manually (and with a large book on linux in my hands) files by files the F...14.04 blocking me and then just had to install (again) 14.04 from my DVD, update and so on. Now this apt up... is working fine except for one stuff : the Trusty-Main 's keys are unknown. And as usuall this probleme is unknown to me too. I think I will have to look at this and as long as this PC work well, have to find tools to avoid the bad situation and to make the "MesSystems" more stable. By the way, do you have some recommendations about this kind of tools ? My Best regards. 2014-06-06 17:31 GMT+02:00 Ding Zhou