You can try to get the bootable Dell Diag disk for the laptop and run the system tester on it or you can try using something like StressLinux or Hiren's BootCD. Hiren's help me find a faulty videocard in a PC a few months ago. The machine would work fine for weeks and then some days it would crash multiple times a day. I also found some other bootable system testers but I can't find the downloads now.