Without an OS installed, a hard drive won't boot.

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How do i install an OS? I only changed the hard drive,i am no expert to other things, everything is shut now and my son needs the laptop for homeworks..can i fix it or i need an expert? 

Thank you 

Ok,so i did good that i bought another hard drive ? Because when i turn the laptop on and i pressF2 or F12 nothing happens

Thanks ejn63 for providing that link. Anything I'm posting with a link is being flagged for administrative approval. So  annoying when you're trying to help someone . 

You'll need a 16G or larger flash drive, and then to download Windows either from Dell or from Microsoft's media creation tool.  Details here:

https://www.dell.com/support/article/en-us/sln297920/reset-or-reinstall-windows-10-on-your-dell-computer?lang=en

We can only point you to the resources you need. After that, it is all on you.

If you want someone to do this for you, you need to go to Best Buy and use the Geek Squad.

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I am guessing you didn't bother reading the link @ejn63  provided.

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Of course i did but i said i am not an expert, i am just a mom that tries to help her son ,you dodnt have to be ironic ,thank you 

Thank you for your help,i will try to do what you all said ,i was only trying to understand if i did good buying a new hard drive or not..because of the pandemic everything is shut now, otherwise i would have taken the laptop to fix

Install of new drive isnt hard when you use OEM system builder DVD.

You set bios sata operation for AHCI and secure boot to OFF.

You install 10 with the "I dont have a key" option.

You press F12 boot from dvd then hit enter when it says press any key to boot from DVD.

https://www.newegg.com/microsoft-windows-10-pro-64-bit-reinstall-recovery-disc-only-no-license-key-included/p/N82E16832350238

https://www.dell.com/support/article/en-us/sln300635/how-to-install-windows-10-from-a-dell-windows-10-recovery-dvd?lang=en

@IoanaA 

Best Buy here in NJ has curbside pickup for repair dropoff. Pretty sure it is like that in other states.

If you get it repaired by them, they will probably want to use their own parts.

Just return the hard drive you bought.