A client had an HP P2-1394 model H3Z88AA desktop system that would turn on briefly, the drives would power up, the fans would spin, and then the system would shut down. After about 5 seconds the process would repeat. This would continue until either the power was removed or the power button was pressed for several seconds forcing the system to the off mode.
Some technical notes found on similar issues suggested the following:
You may be wondering why your cursor keys along with your Home and End keys are not working properly. When you attempt to move your cursor from one cell to another using the cursor keys, the entire spreadsheet moves in that direction. Also the Home and End keys only take you to the far left or right of that row that is currently visible instead of taking you to the beginning or end of that row.
The simple solution might be that you accidently turned on your Scroll Lock. This is a special key that is seldom used today and exists near that upper right of the keyboard between two other keys rarely used, Print Screen/ System Request key and the Pause / Break key. Check your keyboard and see if the light for the Scroll Lock is on, if so that is likely the cause of your issue. Simply press the Scroll Lock key once to turn it off; you should notice the indicator light goes off as well.