The OP is disconnecting the main power connector to the MBoard and reconnecting it while the PSU is on and connected to the mains."
I noticed that. He may have already damaged something as you say.
"Compaq Presario SR1030NX product number DW256A-ABA"
Parts for that model:
"Power supply - 5187-1098 250-watt, regulated (Zinfandel)"
I searched using: Zinfandel 5187-1098
According to this and many other "hits" it is made by Bestec:
Bestec PS models are notorious for being a lot more likely to damage other components when they become defective or fail, usually the motherboard.
Emachines computers commonly use them, and they are probably the most frequent reason for emachines computers failing to boot, even after replacing the PS.
Assuming the computer owner tried a new PS that has at least a 250 watt capacity, if it didn't restore the computer to a working state, it is very likely the mboard was damaged when the Bestec PS failed or became defective from the power outage.
Usually when a PS kills a mboard, the ram, cpu, and the hard and CD and floppy drive are fine.
This is the mboard in this model:
"DW236-69001 Motherboard (system board) - Kelut, GL6E
5187-4913 New part for DW236-69001"
There are often used mboards available on the web for brand name system computers for a reasonable price, say , $100 or less. You could search with DW236-69001 or 5187-4913 or the Presario SR1030NX model number.
BUT make sure the seller states the mboard has been tested and is working - it may have been damaged by a Bestec PS too!!
The advantage of getting the same mboard, other than you can use the same ram and cpu for sure, is it has a Compaq bios version on it that goes along with the mboard model and the original Compaq software installation. If the computer owner ever needs to load the original software from scratch from Recovery CDS, the software will probably refuse to load if it isn't the same mboard, and/or unless it has a Compaq bios version on it, and the Windows software on a brand name system often cannot be used or will not install unless the system has the right mboard model.