I can agree with some of what you are saying about the motherboard (yes, mobo), MB, I/O board, whatever someone may call it. Everything that is "outside the box" be a printer, monitor, scanner, etc. does not draw power from the motherboard, it gets signal from. Usb and firewire powers and signals, 5 volts. Same with mouse/keyboard powered by computers power, inputs signal.
From the original post it sounds like his HP Pavilion laptop took a crap. Usually heat becomes an issue with most laptops (notebooks, or lappys, ha). After 15 years of building computers, desktops and laptops, heat is the most common failure issue that I see. Personally I have a HP Pavillion laptop, no issues, used constantly. My 64bit rig fried a motherboard because of a bad diode. The other three computers, all AMD's run fine (Duron 700, Athlon 1.6, XP2000). Just depends on luck of the draw. RMA's aren't out of the ordinary for a laptop at 1.5 years. 2 computers fried, 1 year, yeah, WOW.
I would question the power source, good ground? Good neutral? Static electricity? Moisture?
Pass on the eMachines. Extra parts bin computers, thats why they are sooo cheap.
If ONE single thing on a motherboard (mobo) fries, chipset, diodes, bios chip, whatever, it will render the computer useless.
I'll bet without model and serial number, the problem is probably a melted heatsink or fried 18v +/- component.