Hi!

If the system unit is really new and untouched after all these years, you
might look at the clock battery on the motherboard. It will most likely be a
round, shiny and reflective silver button cell battery. This battery is most
likely a CR2032.

It is a long shot, but this battery could well be dead. Some computers won't
power up with a missing/dead battery. You can buy one (buy a name brand
battery!) for $2-$3 if you're in the US and probably for a similar amount
elsewhere.

William