Which part should I replace in this case? Hardware and electronics noob :(
If you don't know what you're doing, you shouldn't be doing anything at all with the insides. You're best best is to find someone who has the skills you need.
I don't know my way around the inside of a console either (I've built a half-dozen PCs, but those parts are at least easily replaceable).
Another thing I noticed is that USB Loader always reloaded to cIOS222 r65535 instead of the default 249 even though it was set to 249 in the settings. Even the sysCheck was ok. Does this have anything to do with this at all?
Also is there any way I can extract the saves from my nand backup? Though the saves are pretty old, something is better than nothing.
The computer analogy is good, but would be more accurate if represented by a laptop. Desktop PCs have internal power supplies that connect directly to (in the US) 120VAC and do the conversion & regulation down to something more normal. Most laptops have an external power supply that does the conversion to DC/etc @ that point. This is more on point w/ what the Wii does.
So, to the point, it could be that the power supply (the external brick) fried itself. If you have a multitester, you could check the voltage coming out of the power supply... if memory serves its 12vdc. If you find anything other than that, you have a quandry. There are two ways this could go. Either something external caused the power supply to fail, in which case a new one (easily available) would solve the problem. If however there was some issue within your wii that caused the power supply to fail then it will likely do the same to a new one, in which case you're out the cost of a power supply and/or the friendship of the person you borrowed it from.
My 2c for what its worth.
External Problem - Caused power adapter to malfunction - Caused Wii to malfunction - New power adapter/cable won't switch the Wii on.
Will give it to the game repair store and see what happens. Maybe it's time has come, it's been working perfectly for 3 and a half years now.