Home Built motherboard that is three years old, 500 GB hard drive of unknown brand that is three years old, Unknown power supply, unknown memory but probably 2 GB, Intel dual core 3.16 Ghz CPU, Unknown CPU fan, OS: WXPH with Service Pack 3.
Now tell us what it is doing or not doing?
Do the lights come on for the power supply or motherboard?
Do the power supply fan blades turn? Even 1/3 to 3 turns is important information.
Is there a lot of dirt and dust on the fan blades of power supply or CPU fan?
Have any changes been made to the system recently that would affect any operational component other than the memory?
Do any lights come on for the ethernet socket?
There are model and part numbers on the motherboard... some will be in the center near the processor, and the others will be around the edge of the motherboard. What are they.
When you attempt to boot, what happens, if anything.
What is the power supply power as indicated on the label of the power supply. This label is required for most countries, so it must be there.
The grinding noise could be any of these, and any could cause the stop: Hard drive failure. Power supply failure; DVD or CD drive; CPU fan.
Does it have a floppy drive?
Do you know how to disconnect things. It may be useful to disconnect the hard drive, and boot to a CD disk such as a Windows disk... or to a floppy disk if the CD drive doesn't work.
What we do know if that it can be repaired. We just need more information.