You think you've had problems...
My main computer is five years old and is nearing the end of its useful life. It's a laptop but lives permanently upside down (to help ventilation - it's been overheating) on a desk. The screen is broken and some of the keys don't work. So I have a separate monitor, keyboard and mouse plugged in. I have a fan blowing at the part of the case that gets hottest. Without this it overheats and switches itself off.
I thought a fresh install of Windows 10 might help it run more efficiently and less likely to overheat, so I downloaded the ISO as soon as the final version became available, and put it onto a USB drive.
I removed the SSD and put an old HDD in, so I could go back to my current version easily if anything went wrong. I also made a clone of my SSD onto another spare HDD, just to be extra safe.
I went into the BIOS settings, but it didn't give me the option to boot from USB. So I thought I'd put the clone HDD in and boot from that instead. But that wouldn't boot. I went back into the BIOS settings, and it couldn't find the HDD.
I have a HDD caddy in place of the optical drive, so I put the clone HDD into that, and it booted with no problem. But the wireless adaptor had also broken.
The wireless adaptor is on the motherboard close to where the main hard drive plugs in, so I thought maybe something inside had come loose. I decided to open up the case to have a look. Fortunately I only had to remove around 20 screws, as half of them are missing due to previous repairs I've made. Still a pain in the arse trying to get into it though.
When I eventually got access to the motherboard I couldn't see anything obviously wrong. With the computer still in pieces I went into the BIOS settings again, and it still couldn't see the main hard drive or the USB stick.
I was seriously pissed off by now, so I ordered a new (refurbished) laptop from ebay, which is due to arrive tomorrow.
After leaving the computer for half a day, I decided it might be a good idea to put it back together again. I couldn't be bothered to take much care when screwing everything back together, so I had 10 screws left over when I finished. Nine on my desk, and one somewhere on the floor.
I switched it on, and it now recognised the main hard drive, and booted up. The wireless adaptor was also now working.
After I'd finished banging my head against the wall, I went into the BIOS settings, and it now allowed me to select the USB stick as a boot device.
So I booted from the USB and did a clean install of Windows 10. It installed surprisingly quickly, and then asked me for my Windows product key. This surprised me because I thought it would just use the key that's embedded in the bios. I knew my key anyway, so typed it in. Windows 10 said it was an invalid key. It did let me skip this though, so I skipped it, and was able to use Windows 10. I then Googled the product key thing, and found out that you can't do a clean install of Windows 10, without first installing Windows 10 as an upgrade, and then activating it.
I'd done the clean install over the top of my clone HDD, so I had to create another clone so I could do the upgrade on that. Then I ran the upgrade, and everything worked.
When I had the laptop apart I cleaned the heatsink which was clogged up with dust which prevented a decent flow of air. Since then it's not overheated, even when I've turned off the external fan.
As Windows 10 was on a HDD rather than a SSD, it's a lot slower, so I've put my SSD back in and I'm using Windows 7 at the moment.
So I'm now in exactly the same position as I was before I did any of the stuff above, but my computer isn't now overheating, and I didn't need to waste money on a new one.