A technician worked on my HP Probook running Windows 7 pro and installed an OEM OS without telling me. I didn't find out until I tried to upgrade to Windows 10. I have the key for the old license on the COA. Can I still upgrade without re-buying the license for 7, or am I out of luck?
It depends, by OEM do you mean the technician installed a pirated copy? Did you download the "Get Windows 10" application and it's not letting you update telling you your copy is pirated or why is it failing? A few months ago Get Windows 10 was updating even pirated copies of Windows 7 into fully legal Windows 10. I don't know if it's still doing this, or whether this was intentional. It could be in line with Microsoft's policies to get as many people to use 10 as fast as possible. Also, if the OEM is not working do you have your old system to reinstall? If you have the product key, you can also download a CD from Microsoft to reinstall your old system, in case the OEM doesn't work.