CLKD, is it during your recent depression that you've been unable to recall happy moments, or has it always been like that?
I can have total recall of happy moments, but it usually needs a physical 'trigger' - something I can see, taste, touch, smell or hear. For example, a stone brought back from a holiday in NZ 10 years ago - holding it brought back total recall of the day I found it. I can usually bring up the memory and feeling deliberately, if it was a strong one, although the 'best' recalls are always the ones that arrive unexpectedly.
However, following my father's death, I lost this ability for several months. I would look at a photo or touch an object and think 'yes, that was a happy time', but it was just like saying 'yes, that is a large blue notebook' - it was a statement of fact, but I had no emotion connected to it. Looking back, I think I was suffering from depression at that time. I can often lift 'ordinary' down moments by recalling good times, but it just didn't work then.