Major PC hardware failure

Greetings,

I built a pc around Pentium cpu, Intel D865GVHZ board, Antec case/PS back in '06.
Have been running it about 16 hours/day ever since.

Whilst running a backup Sunday, I heard a constant little tic-tic, tic-tic,
tic-tic sound, looked down to find Speedfan registered about 74 C., then watched
the W2k system crash.

I immediately suspected a cpu fan failure, but all fans were running when I checked.
I've now replaced the cpu fan/heat-sink and the power supply.

The system gives the following message:

"The CPU was previously shutdown due to a thermal event(overheating)
Service the unit right away to resolve this"

and soon shuts down all power.

I need to restore the system to functionality, but hardly know where to start.
Any/all help would be much appreciated.

TIA,
Puddin'

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."