Re: Using Android Kit-Kat on the PC
So you installed Android over an existing Ubuntu partition on your drive? Without knowing the details of your current configuration and desired configuration it's hard to advise one way or the other. Are you receiving any errors when you attempt to boot? Which partitions, if any, are left intact? Any problems with your MBR are more likely a result of the Android installation and related steps than from powering off your machine with Android running. Installing Android with GRUB over an existing MBR partition will remove the MBR table; I suggest using EasyBCD or similar to set up a valid MBR (manually
Do not attempt to manually recreate/recover a previous MBR (first 512+ bytes of the first sector, consisting of partition table + bootstrap + timestamp + signature) unless the partition environment is unchanged and you are comfortable with manually manipulating MBR/GPT configurations. It's worth knowing about GPT; this section in particular can be helpful when navigating MBR/GPT issues with multiple operating systems:
See the GPT diagram on that Wikipedia page if a visual representation might be helpful. Android x86 can be installed in both MBR and GPT UEFI environments, so just be sure to look into any differences in your environment from any instructions you may be referencing. I'll link you to these for now... there are resources, files, and steps that may be of some help depending on what you'd like your final setup to be.
Traditionally, in IBM PC compatible systems the first sector of the disk holds the Master Boot Record (MBR), containing the drive's partitioning information and the code of the first stage boot loader for BIOS-based systems. For limited backward compatibility, this sector is still reserved for a MBR in the GPT specification, but it is now used in a way that prevents MBR-based disk utilities from misrecognizing and possibly overwriting GPT disks. This is referred to as a protective MBR.
[GUIDE] Installing android x86 without CD or… | Android | XDA Forum
[android-x86] Problem while booting pc [android x86 boot error 15] - Grokbase
linux - Remove GPT - Default back to MBR - Unix & Linux Stack Exchange
This link also has succinct information on managing, backing up, and restoring MBR tables: