Latitude D600 would not start up (not A/C adapter or battery) - working now...

I have a very old Latitude D600 (~2005) that was working fine one day and then the next day it wouldn't start up. When I press the power button it would only flash the power light on for about 2 seconds, and then it would switch off. However, when the power light came on, nothing else came on, no screen backlight, no fan, no hard drive, no other lights. It seems like something is failing during POST or something.

I tried another A/C adapter, tried taking the battery out, nothing worked.

That was on Friday. Today, Monday, it's switching on fine, although Windows says it has recovered from a serious error. The link to the MER website said that a device was failing.

Any ideas? Or since it's working for now, should I just keep an eye on it?

Seth