HSF = Heat Sink & Fan. You need to check for bad capacitors on the motherboard, Look very closely at the cap's and see if there are any with the tops bulged out or if there are any leaking. A leaking cap looks like a white power build up and rusty looking deposits and if they are really leaking there would be a small amout of a oilly looking substance as well. It would be nice to test a new power supply in there as well. You don't need anything fancy in that socket A something like This silverstone would be fine
To check your temps and voltages you can try the msi tools listed on this page MSI
And do you have the latest bios for that system? It's 1.c 2004/11/01 Latest bios
but with all that said you can pick up a nice socket A board at a mom and pop pc store for about $60 Like the asus A7V8X-X And i agree with you that probably is what's wrong.