I upgraded two old Dell optiplex 990 and basically threw everything out except the mainboard. After I finished and was about to install Windows but every time I tried it aborted saying "windows failed to start a recent hardware or software change might be the cause". I didn't think much of it and just installed windows onto the SSDs using my main PC. But now the PC spits out a "no bootable devices found" for around one frame and then it shows the windows loading screen also for just one frame. After that the "initialisation underscore" keeps blinking indefinitely.