Before you download Windows 10. I strongly advise you to check with your computer manufacturer that it is suitable for it. Do not assume, as I did, that if you have Windows 8.1 that you are OK to use Windows 10. because you are not, so better to check it out first. My 2 year old Acer Laptop stopped working , completely froze up, shortly after the free download. I contacted Microsoft whom informed me that my Acer model number was not on their list of suitable machines to use Windows 10, and suggested I contact the manufacturer Acer. Contacting Acer they investigated the model number and informed me that Windows 10 is not suitable for my Laptop. I am now using my old XP desk top computer until I can collect my Laptop from the local computer repair shop, where hopefully, it will have been restored to Windows 8.1 and back in full working order, not checking my Laptop's suitability for Windows 10 was an expensive oversight on my part.
Just received a call from the Computer Repair Shop, it seems as though they have managed to restart the Laptop on Windows 10, and I have requested them to leave it on Windows 10 if it OK. They believe it could have been a virus, so will check it out throughly and make sure Windows 10 is working as it should before I collect it. I think it is still worth checking with your computer manufacterer before downloading Windows 10 just to make sure it is suitable.