car not open with phob or key

[Tommys A5 Quattro]

hi hope I can get advice on this ??

I went to unlock my car this morning (cold and frosty) the phob not work could not open the car at all  Red light on the phob still flashed .even the key would not unlock the door !!!.had to get a lift home from work . 30 mins later went back to the car and it had opened even the boot . a strange one .why would the actul key not unlock the drivers door do you have to do anything when trying to use the key any ideas would be grateful cheers