and welcome to the Forum
A couple of things . . eMachines were hit hard by the bad capacitor problem . . look closely at the board to see if any are ruptured or leaking;
For more, see
this
eMachines are also notorious for their poor Power supplies . . regardless of how it tested, I would not risk a new motherboard.
Can you give more details on the old board . . what processor model and what kind of memory. You should be able to find a Brand and model printed somewhere on the board
Edit . . I googled the model and find it uses an Intel Intel D845 processor. If you can find a board that uses that processor it should work . . but it ain't gonna be easy finding one