HPenn
Ordinarily, what I would recommend is ordering HP Recovery Media to restore the PC.
But there are two problems in this case. First, there are over 200 models of that desktop, and without the model number, I can't check to see if recovery media is still available from HP.
Second, if it is not, you would have to go to a third-pary to order the media from them, and for that, you would need the specific model number.
If you can find the model number on a sticker or plate on the PC and post that, I can check for HP media, but you can also go to these sites and checks yourself if they have the media for that PC: http://www.computersurgeons.com/ and http://www.restoredisks.com/
Recommending this because it's generally a lot cheaper than going out and buying a copy of Win8.1.
Also, as an alternative, you can use RUFUS to create a bootable USB stick from the ISO you have and see if this PC boots from that -- realizing that the HP OEM product key on this PC is most likely NOT going to work to activate the Win8.1 you install from the ISO.
Good Luck
I am a volunteer and I do not work for, nor do I represent, HP.
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