Windows 7 Ultimate 64 bit iso image with SP1... can't find US English on Microsoft Web site, closest is Serbian Latin --- found version of SoftLay.net ... is it a valid copy?

I have a retail version of Windows 7 Ultimate 64 bit on the computer in question, not an OEM version.

The download link I gave you is for Windows 7 ISO downloads for OEM and Retail Licenses

I have a retail version of Windows 7 Ultimate 64 bit on the computer in question, not an OEM version.

You can download SP1 here. 

EDIT:  You can follow the instructions here to slipstream SP1 into your installation media.

I have a retail version of Windows 7 Ultimate 64 bit on the computer in question, not an OEM version.

You can not replace the Motherboard with an OEM preinstalled License with whatever Motherboard you wish to when you have a preinstalled OEM License (HP, Acer, etc)

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You have to follow the directives or you void your OEM License; IF you have an OEM License.

This was the original link. Microsoft is altering/deleting links, but the information that was originally there remains the same (I copied it before the link disappeared)

http://www.microsoft.com/oem/en-gb/licensing/sblicensing/pages/licensing\_faq.aspx#fbid=iePP5a9JaWJ

Q. If my customer asks me to upgrade a PC with new hardware components, when is a new operating system needed? When would the PC be considered "new"?

A. Generally, an end user can upgrade or replace all of the hardware components on a computer—except the motherboard—and still retain the licence for the original Microsoft OEM operating system software. If the motherboard is upgraded or replaced for reasons other than a defect, then a new computer has been created. Microsoft OEM operating system software cannot be transferred to the new computer, and the licence of new operating system software is required.

If the motherboard is replaced because it is defective, you do not need to acquire a new operating system license for the PC as long as the replacement motherboard is the same make/model or the same manufacturer's replacement/equivalent, as defined by the manufacturer's warranty.

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If you bought and installed your own Retail Windows License, you can change Motherboards, but doing that will now require a Phone Activation and you should not follow the Auto prompts, but hold on for a real person to explain to.

Download the correct ISO file and make your own disk and use the Product Key that is on the COA Sticker.

https://www.heidoc.net/joomla/technology-science/microsoft/67-microsoft-windows-and-office-iso-download-tool

Download: Windows ISO Downloader.exe

Version: 6.00

Release Date: 11 April 2018

Requirements: Windows 7 or newer, .NET Framework 4.x, Internet Explorer 8 or newer.

Important: As of Version 6.00, we're adding back an experimental feature to generate links for Windows 7 and Office 2010. Generation of new links for these products is throttled, and not every download is always available in every language. New links are generated on a first come first served basis, with users who enable the idle resource donation getting preferential treatment. If you have further questions, please use theWinCert Forum to get in touch, so that other users can also benefit from the discussion.

And here are instructions on how to burn ISO images to disk:

http://www.snapfiles.com/get/ISORecorder.html

You change the Boot Order in the BIOS to be able to boot from your installation media:

How to Boot Your Computer From a Disc or USB Drive

Then do a clean install:

http://www.sevenforums.com/tutorials/1649-clean-install-windows-7-a.html

The COA sticker is either on the underside of the Laptop or in the Battery Compartment.

With a Desktop it is either on the side, rear or top of the Computer Case.

Using the downloaded ISO file Method may require phone Activation.

If it does require phone Activation, do not follow the Auto Prompts, but hold on for a real person to explain to as to what has been done for re-installation purposes

"How to Activate Windows 7 by Phone"

http://www.sevenforums.com/tutorials/18715-activate-windows-7-phone.html

The above method also will require you to go to your Computer Manufacturer's website > Support and Downloads Section > locate your Model Number and Operating System > then download and install the latest Drivers for it.

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Using the USB method in conjunction with the above Windows 7 download:

http://www.sevenforums.com/tutorials/2432-usb-windows-7-installation-key-drive-create.html

"How to Get and Use the Windows 7 USB/DVD Download Tool"

http://www.sevenforums.com/tutorials/31541-windows-7-usb-dvd-download-tool.html

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And this is very good and easy to use:

Rufus - Create bootable USB drives the easy way