I have a very old Dell Inspiron 8500 laptop that I've recently set up to use as a secondary computer. The batteries that I have for it are all permanently dead, so it runs entirely on AC power. Occasionally, it will randomly power itself off. When this happens and I turn it back on, it often powers itself off again immediately. The automatic shutdowns most commonly occur when the laptop is on a surface where there is movement, such as my lap or a couch, rather than when it's still (although it did once shut itself of when sitting on a table being completely unused). I can tell that it's not a case of the AC adapter plug simply sliding out of the unit though, as it always appears to be firmly inserted after the shutdowns. Is this likely a problem with my laptop's power supply, my AC adapter, or what?