I just buying a new laptop hp 640g1 with hdd 320g.
After installing manjaro kde it works well but when i shutdown the laptop stop for 15 seconds and open again i tried install windows and works well its not open after shutdown and another problems when install manjaro xfce it gives me that no os and 3f0 .
*the problem of shutdown its happen in all linux distros.
Can you check the Bios settings of your laptop ?
You should change the following settings:
Change Boot mode to UEFI Native
disable Fast Boot
disable PXE Boot