The most likely reason is that the drive was formatted with a Linux file system. Reformatting the drive to NTFS or FAT32 will make the drive usable in Windows. You could also install an ext4 driver in Windows to access the drive without reformatting it.
Yes it will also work with linux.
Just mount it as you would any drive.
You can certainly move Windows to an external hard drive but Windows will not boot directly from an external drive. If you are running Windows in Parallels (See links below) you can have Parallels installed on the Mac's drive and then have your Windows virtual machine on the external drive.
Have a look at WUBI (search Google) to install Ubuntu as a file, without making any changes to your Windows 8 hard-drive. To remove WUBI, simply use Windows utility to uninstall programs. Or, create a separate partition on the Windows hard-drive and install Linux (or which ever distro you wish to use) on to the new partition. Remember to first backup important files onto an external storage device. Or, download and burn a Linux distribution with an ISO extension onto a CD and use as a Live Disk. If you then intend to install Linux, you will be given the choice to either install as a dual-boot with Windows by installing Linux alongside Windows, or wiping Windows and letting Linux use all the hard-drive.
In our old computer I put a SEAGATE 500 gig External Hard Drive. The computer was windows XP Is it a working chance to use the external hard drive From The system i first installed it.
No. Installing Linux is no more destructive than installing Windows.
MS is nasty and try very hard to make things incompatible, but generally linux can read and write windows drive.
try Linux it always works for me
Format the hard drive, install another version of Windows, or a Linux distribution.
When selecting the drive you wish to install the OS on, simply select the external HDD.
Unless you already have a free partition on your hard drive or an additional hard drive, you cannot install Red Hat Enterprise Linux without "disturbing" Windows; you will need to resize the Windows partition to make room.
Yes you can, when the computer is booting up open the boot menu and choose the external as your boot device, i have a external hard drive with Ubuntu on it and do exactly that, I'm sure it can work with windows.