System Reboots instead of shutdown when shutdown key is pressed !!
I experienced exactly the same problem on my new computer Intel i5-4440 processor and Intel DB85FL motherboard (4th Gen). First I faced this problem with Ubuntu 13.10. and subsequently after upgrading to 14.04 LTS.
I did the following recently to solve this problem of SHUTDOWN and automatic REBOOT again withing a second or two.
I have Intel Visual BIOS. On power up I pressed F2 > POWER > Wake On LAN from S4/S5.
This has 3 options.
1. Stay Off,
2. Power on – Normal Boot, and
3. Power on – PXE Boot.
My computer was set to #2, which was making it automatically REBOOT after SHUTDOWN. I now changed to #1 option mentioned above. Now it is okay.