Looking for installation for customers computer

the customers hard drive completely died and i purchased a new harddrive just need installation media to reinstall os

Dell stopped providing installation media for Windows 8 after Microsoft ended its support on January 2016.  You may however, search for the media on auction site.  

is there a way to see what os it originally had?

i install it and the key is not automatically activating

Go to Dell Support site, you can enter the service tag into the box to identify your product (do not post it here).  At the result page, select View Product Specs under quick links.  Expand all and you should find the OS the system was shipped with.

would any dell windows 8 recivery cd work?

Any of Win 8 installer should work.  But, the license key is embedded on motherboard and should not giving you problem for activation.  Verify if the system was actually shipped with Win 8 originally.

@Chino de Oro​ its showing windows 8

i get "this product key doesnt work 

Sorry, but you are repeating the issue you have already stated instead of verifying what was the OS shipped with the system originally.  You may try to download and reinstall using the OS recovery image from here  https://www.dell.com/support/contents/en-us/article/product-support/self-support-knowledgebase/data-storage-backup-and-recovery/backup-recovery/Media-backup .  Due to the end-of-life for legacy Windows supports, some of the recovery features may not be available anymore.