Idiot of the year award - Atari 800 help please

I think I deserve some kind of award for what I just did..

I unpacked my old Atari 8bits -- a couple of 800XLs, and old 800s I also had while growing up.

In the process of checking everything out, with the machine powered off, I plugged a Spy Hunter cartridge into the RIGHT cartridge slot of one of the (original) 800s..

The original Atari 800 was working but will no longer power on..  

Any ideas what I may have damaged?  

Thanks,
John