I used to work at a very large company that produced laptops. I did line testing. You have no easy way to diag this since you don't have access to any documentation. A scope or vom might lead you to power in some areas. Knowing from web reports might lead you to common parts. Each laptop is unique. There is no standard. Some Dells might have known on off switch issues or dc to dc issues.
At this point taking it apart is unknown. We don't know that Compusa did. You do need the correct PSU. Some of them are actually smart psu's and not interchangeable. I guess it can't hurt to carefully peek. Some ants could present an issue. Usually only fire ants and not regular sugar ants. If they built a nest maybe.
Best to see if anyone sells cheap parts before you get too far along. HP wanted like $300 for a laptop motherboard and a complete new system wasn't that much more.
If our Alphas ever go out I'll contact you, we got rid of our Q-bus systems.