brancamonti :
I need to repair a computer's OS, I know it has Windows 8/8.1 but I'm not exactly sure. My question is: Can I restore win 8 home with a win 8 pro .iso and vice versa? what about win 8 with win 8.1 .iso?
The short answer is: NO.
You must use the media version that was originally installed on the mainboard BECAUSE the windows 8 / 8.1 / 10 keys are 'injected' into the mainboard during installation. There is no license key sticker for these versions of Windows.
You can use this
LINK to download the media creation tool from Microsoft. It should give you options during the set up as to what version of the Windows 8.1 you want to create.