Background: The desktop is about 14 years old. I look at old files from time to time and it has worked fine (but very slow) up until the other day. I can get into BIOS, which I reset to the default, but not into safe mode. When I turn the computer on it starts loading as usual. The Windows logo comes up then it goes into a black screen while it loads. After about a minute, when it should start populating the icons it appears to shut off and then immediately turn on again and repeats this cycle over and over. Any ideas what it could be?