2006 2.5L new beetle power out while turning key, what's the problem? Thanks.

Hi, we got a 2006 2.5L new beetle. Up till recently the car runs fine(although the road noise is kinda high). This morning when I turn the key trying to start the engine, half way till the start position the power suddenly cut out. When I just started turning the key the power was there(on the dash) but then it was completely out. The starter didn't turn because there was no power. The car's completely dead. Then I tried to start again still no power, as if the battery's dead. Frustrated, I came out of the car and trying to get a jump cable. When I came back with the jumping cable, I thought what the heck let me try once more. Then when I opened the door the power's back(the dash lights up again) and the car then started normally. I opened the lid and found the battery connections are secure(they are not loose or anything). What could be the problem? Is it one of the solenoids reached it's end of life? Could someone shed some light on this? By the way this morning it was kinda cold at 39 degrees but it was a normal autumn morning. The car has been running just normal since.

Thanks for the input.