Guni,
3) It can be both of 1), 2) that depends on context.
memory......the ability to remember things
memory.....something that you remembered
1) I have a bad memory......my memory doesn't function well.
2) I have a bad memory......I have an unpleasant memory of some past event.
1)
Doctor - So, you are here because you have a bad memory?
Patient - Yes doctor, I can't remember anything. In fact I have such a bad memory that I forgot why I came to see you!
2)
Psychiatrist - Today we are going to discuss your childhood memories. Do you have a bad memory you would like to talk about?
Patient - Yes, I have a bad memory--a very bad memory about my first day in school.