For the past 1 week, I have had Xmas lights hooked up to the outside electrical socket. Less amount than last year without any issues. I had it hooked up with sun timmer and just noticed that they didn't turn on tonight. I try a GFCI tester and it indicates open hot. It indicates this on my front and back outside electrical recepticles. I don't notice any other issues with other electrical stuff at home right now. I don't see any breakers flipped at this time.

Any idea on what could be going on?

Are the outside receptacles GFCI outlets or protected by another GFCI outlet or GFCA breaker? Is there a GFCI outlet tripped possibly?