if the motherboard had a short in it putting it outside on a piece of cardboard would see if its a short, now that you said you have been having electrical storms that PSU probably took a shit. And just plug that HDD in to another PC and just grab the info. Make sure in your bios when you do have it installed to make sure it doesn't use that HDD as a boot drive.
Lets hope that PSU didn't take the HDD or something else with it.