I have a tenant that called and said that his AC thermostat keeps resetting his settings. When the unit finishes its cycle, it will reset the temperature settings to the default setting. Any ideas as to what is causing this? How can I fix it?

Hello, first post here from a weekend DIY'er. Please excuse the length but I've been spending many hours on this and really need your help. A string of 7 outlets across 3 rooms (living room (2), spare bedroom (3), bedroom (2)) stopped working recently. The unit is about 11 years old. I've tested all the GFI receptacles and verified that they are all working and not tripped. I've also searched the unit for any hidden GFI outlets (including outside) but could not find any others except the 2 in the kitchen and 2 in both bathrooms. I began to go through each receptacle to test power and noticed that one of the non-functioning outlets in the spare bedroom was split so that the top was fed by a red hot wire and controlled by the light switch (working). The bottom had a black hot wire going in (not working). When I replaced the receptacle with a new one, I did not remove the tab connecting the hot wires, so when I turned the circuit breakers back on, not only was the bottom working, but all the previously non-functioning outlets had power! When I broke the tab off, the outlets stopped working again. I also checked the wire nut for the black hot in the junction box but my voltage tester did not show any power going through any of the black wires. Picture of spare bedroom receptacle [IMG]http://i877.photobucket.com/albums/ab332/ironchefm/DSC_0938.jpg[/IMG] I'm guessing all the other outlets are downstream of this bad outlet. However, could the problem with the black hot wire be traced back even further, possibly to the panel? Should I continue to check all the other bad outlets to see if one had power coming in but no power going out? I haven't done this earlier because some outlets are behind heavy furniture. Note: also understand that those backstab connections need to be replaced to real ones but want to restore power first! :) Any help is much appreciated! Thanks!