Problems with my electrics

I have a 307 2004 plate. Today, the dashlights and headlights went off while driving and then came back on again. This evening, on my way home, the same thing happened but when i started my trip, the driver's door wouldn't open and i had to use the key to open it and i had to push it hard to open when i wanted to get out. I thought it might be a fuse issue but on reading some posts, it seems it may be something else. I've had the car for 14 years and this is the first time it's happened. Can anyone help me with a diagnosis please? The batteries were replaced last year, so i don't think it's that. I would appreciate plain English please as the mechanic speak confuses me. Thank you in advance.