MBP Boot problems

I got my 2007 MBP back from the Apple Store today, where they fixed a fan that was spinning out of control. When it got back home, it would connect to my network but couldn't get an internet connection, even though everything else on the network was fine. Trying to fix that led to the revelation that System Prefs would stop responding every time I loaded the Network prefpane.

Tried a safe boot to see if some app or other prefpane was causing the crash, and midway through Safe Mode's disk check, the screen just went black. The system wasn't plugged in, but had ~50% battery. Now it doesn't boot. Plugged it in, just in case something went weird with the battery, to no avail. Doesn't light the screen, spin up the drives, nothing. Just stays off.

Solutions or tips much appreciated, or this'll be it's third time to the Apple Store in as many months.