Vaio VGN-Z690 Shuts Off Randomly After Short Fall

My girlfriend's VGN-Z690 took a small (about a 2-3 foot fall onto a short pile industrial carpet. fall the other day. The only visible damage it to the top left of the lid (which has a crack and the tab the holds the lid together there broke off). There is no other outwardly visible damage whatsoever.

Since then, the computer shuts off (power completely shut off) randomly. Tried using it with and without the battery and with and without it being plugged in. Sometimes it runs for only a couple minutes and sometimes for several minutes, but it always ends the same way. All this while only browsing the internet over WiFi (suggesting it's not overheating).

The laptop is still covered by 2 years more of on-site warranty, but doesn't have the accidental damage coverage, so I'm thinking I'll have to try to repair this myself.

Any ideas as to what might be the problem? I've read in the forum where a loose cable can cause this behavior, but am looking for your suggestions before I open it up. What would make it abruptly shut off like that? What could be jarred loose on the inside from a fall that was insufficient to present any significant outward damage?

Thoughts?

 

Don't dismiss overheating as a possible source. If the heat sink has been knocked loose by the fall, it can easily overheat even when not running a high load.