How to reformat external hard drive from mac to windows?

Added (1). My mac book crashed so I transferred all my data onto an external drive (computer repairer took out the hard drive in the computer) but then one day it started working again, but only if the external drive was connected. I bought a new windows laptop (lenovo G50-30) and I can't see the external drive anywhere when plugged in - not even in disk management. I can't see it on my mac either so I can't reformat it to use on my new laptop. Someone help me please! Basic instructions appreciated!

CEF

Don't see what this has to do with Society & Culture > Religion & Spirituality

Guest

When you reformat your hard drive you are changing the format of the particular partition. There's no "Mac" or "Windows" format. Formats include things like NTFS, FAT32, FAT16, etc. After you format the disk, you get an operating system on it by installing the file system. If you have something like a Windows or Mac installation CD, you should be able to install the file system onto the formatted external hard drive, although what the installer is capable of depends on the individual installer. Might I recommend Linux instead?

Amelia