Original window8 OS lost, how can I get my product Key

I have moved this to the Microsoft OS Forum.

You need to call Dell Technical Support for Saudi Arabia and request a Windows 8 Reinstallation DVD or Recovery USB. I prefer the DVD as it can be converted into a USB and allows for a proper clean installation. The USB on the otherhand will have the likes of preinstalled drivers and McAfee integrated which can cause later issues with Windows Updates.

http://www.dell.com/support/contents/ae/en/aedhs1/article/Contact-Information/Technical-Support/technical-support-phone-numbers

Regarding product Key Windows 8.0 media will automatically detect and input your Windows 8.0 BIOS Embedded SLP key during installation. If you need to find the key you may use RW-Everything:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/obtaining-your-oem-bios-embedded-slp-product-key-using-rw-everything-oem-only/

If trying to install Windows 8.0 with a Windows 8.1 .iso note that Windows 8.1 media rejects Windows 8.0 product keys and vice versa. This limitation can be overcome using a generic key for installation and change key for activation:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/installation-of-windows-8-1-with-a-windows-8-0-retail-product-key-notes/

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/product-activation-using-a-windows-8-1-product-key/