Thanks to readers K. A. Hruzer and Steven Roemerman for writing with tips on diagnosing my poor laptop's problems. It was reassuring to see that both had similar thoughts on what could be wrong. I've tried reflashing the BIOS to no avail, as well as disabling everything in the BIOS that I can find to disable. I replaced the memory. It passes Dell's diagnostic suite. The next thing to try is replacing the reserve (CMOS) battery, which powers the clock, the BIOS, and the NVRAM. I will keep you posted.