Welcome to G2G Kamau
From the little I've been able to find out in google, it looks like the motherboard is a socket 7 board with a AMD K6 500MHz cpu. This explains why there is I assume from what you said, that the machine stopped working after the grandfather moved it to a different case, right?
If so, then please follow these instructions VERY carefully. Before you start, make a note of how the front panel connectors connect to the motherboard (i.e the front power switch, case speaker, reset switch, power LED etc).
If you have any questions, please ask.
1) Wear an anti-static strap or at least discharge your static by touching a metal surface just before opening up the case. Disconnect the external power lead & peripheral devices, then disconnect the PSU connectors from the motherboard.
2) Remove the pci cards & drive cabling etc, then remove the motherboard from the case. Leave the cpu+heatsink/fan in place. Make sure you place the components on a'safe' surface such as paper or card. Do not put down down on carpet for example! Also make sure you avoid touching any of the metal contacts on the cards.
3) Whilst the board is out of the case, take this opportunity to make sure that ALL the metal spacers (stand-offs) in the case line up with screwholes in the motherboard.
4) Place the motherboard on either card or a thick pile of matt paper. Ensure that the underside of the board is completely insulated by the paper/card.
5) Check to see that the heatsink assembly is fitted correctly & securely. Do not remove it however unless you need to. NB. heatsinks for these cpu's will often fit either way round but only one way is correct.
6) Remove the ram modules. Regardless of how many ram modules there are, just re-insert one of them (in the ram socket nearest the cpu). Make sure that the module is the right way round, open the two plastic clips at either end of the socket, then insert the ram module by pressing down evenly on both ends. Do not force it though. If it is correctly inserted, the two plastic clips should spring up & lock in place of their own accord.
7) If the system has an add-on video card (agp or pci), as opposed to an integrated one, then install this next. Again make sure that both ends of the card are evenly inserted in the socket.
8) There should be a flat round silver battery somewhere on the board. Remove this & leave it out for about 30 seconds, then reinsert it. The + sign must be on the top.
9) Reconnect the power supply leads to the motherboard. (Do not connect any drive cabling to the board though). If you have any doubts about any of the power connectors, then please ask first.
10) Reconnect the system (case) speaker to the front panel header on the motherboard. Reconnect the front power switch connector to the motherboard. If either of these two will no longer reach the board while it's out of the case, then let me know & I'll talk you through what to do.
11) If speaker & power connectors reach ok, then reconnect the monitor, keyboard & external power lead. Boot the system up & let me know what happens.