G505 has no power - won't start

I have a Lenovo G505 that recently appears to have died and I can't get it to start up.  I initially thought it was a bad AC adapter and replaced that, but even with a new adapter I don't get any response from the laptop.

I tried removing the battery, removing the power plug, and holding the power button for 20 seconds.  Nothing changed.  I tried removing the battery altogether and powering it on (thinking that it might be able to run only on AC power) but that didn't work, either.

I don't get any sort of power indicators anywhere - no LED lights, no sounds of it booting, no BIOS, nothing.  It's like it's not getting any power at all.  No matter how long it's hooked to the AC adapter, I press the power button and nothing happens.

Is there any further advice or anything to try, or should I just call it dead and start looking for a replacement?