Pc suddenly requires my western digital to be formatted

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I had a similar problem with a drive recently, and found that Windows chkdsk was able to fix it....

Have formatted this WD external hard drive? Or have rescued everything desired back with luck?
If you are still stuck in such drive not formatted error, you can try data recovery software to take all left drive stuffs back and format this drive latter to remove the not formatted error problems.
To rescue your drive information, learn more detailed steps here:
How to restore data from hard drive that needs formatting
Make drive data backups well to avoid such unexpected drive errors in the future.

There are chances you can have all your data back. Go for the tools that help you recover your HD. DONOT overwrite anything on HD. Data Recovery Services will guide you in this. You will be helped by free consultation. So don't worry about your stuff. http://www.stellarinfo.co.in/services/hard-disk-recovery.php

Though the PC is asking you to format this external drive, your remained drive files are still left on that drive and are possible to be restored back with data recovery software before they all are overwritten or damaged.
So, don't worry! Stop using this drive and search for reliable data recovery software to take your drive files, images, videos and more back.
Here is a video tutorial that can teach you some details of drive data recovery:
https://www.youtube.com/watch?v=NB5QtjzKqGI
Act carefully from now on.

The drive is likely failing; Windows is unable to located a boot record for the drive and therefore it wants to format it in order to continue; trying it on a 2nd pc confirms this.
It may be possible to use a utility such as Data Doctor's Data Recovery to recover the data but it's going to cost some $$.
You can check out the utility at http://www.software.com/view/8432/0/data-doctor-windows-data-recovery-software
I've used this in the past to recover data from drives that were overwritten; and to undelete files that were lost when someone accidently deleted a user's windows profile.
Hope this helps! good luck!