Frankly I don't really care, but I'm completely confused: I thought your drive died. Now you wanna test your MB?
You are aware of this is a bit more ambitious job than looking for why your egg cooker doesn't work? You need a bit more than having some YT videos watched and a voltmeter from the supermarket to do that.
Anybody does/did electronics on a professional level will tell you: Don't waste your time on that. You will slave months over it, if not longer, with no realistic chance of success.
If the whole machine is powerless, you may check some capacitors, diodes, fuses, inductors, connectors and conductor lines directly at the board's onboard power supply circuit. But anything else ain't even remotely worth the effort: too many (tiny) parts on a multilayer PCB with no scheme at all, some even covered under lacquer paint, so no connection for measurement... - not a chance to find all parts to be suspected in a reasonable time.
Even if you figure out the voltage provided at the drive's port was too high - which I highly doubt very much, because those are all standard ICs used and working properly and reliably millions of times - then what?
Look close at your PCB's ICs! How many of them there are? Which one is for the port's power supply? What type of part exactly is it? What's the part's type designator? [Not the serial number, nor the lot charge; if there even is something readable written on it.] Even if you found and figured that part out doubtless, where do you get this part from to replace it? I bet, even if you make it that far, you will not get this part anymore. Especially when the machine is older than 3...5 years most of its ICs are not produced anymore. You need similar same luck like winning the lottery to find one to be bought at Mouser, Digi-Key et al (they name lots of parts in their catalogues, but most are out of stock, and forever will be) - if those were even available on the market anyway, and not exclusively produced for or even by the laptop's manufacturer itself (many of those have their own semiconductor fabs producing only for their own usage.) With extreme luck you may find some remainders offered by an IC broker. Of course then you need to buy them all: app. a couple of some hundreds to a few thousand parts for way more than you get a couple of new laptops for. When you get the part, which I doubt, then what? You replace it with the new part, of course. Ever compared the tip of your soldering iron with those connector pins? But many ICs, especially power supply ICs, come as BGA - all (and many) connectors are under the part. A soldering iron is completely useless here and can only cause damage. And even if you got this far there is a very high probability you will face the bitter fact, you still did not repaired your machine. Because chances are high, that's not the only part damaged, and chances are even higher you do even more damage to your board than repairing.
Then you want to replace the motherboard. I got it right: We are talking a laptop here, right?
With laptops it's not like desktop PCs, where the MBs come in standard ATX sizes. Most laptops have an individual tailored, own designed PCB. The only way to get a fitting replacement is to get an identical laptop. Then you use that, but don't exchange the boards - which with laptops is very much more fumbling than with a desktop/tower PC; it's not that simple like replacing its SSD, RAM or WLAN module.
Maybe I'm mistaken, and you are an experienced electronics hardware master with pro equipment.
But if not, take my advice and don't waste your time on that.
My guess is, there either was some static electrical discharge, which toasted your hardware (maybe you touched it without being properly grounded), or it died of other ("natural") causes.
Sooner or later hardware also just dies by age. Then it's time to get a new one.
But trying to repair modern electronics instead of trashing it may be a noble idea, but practically it's a waste of time, resources and money.
