Goro is probably right with the advice not to put it in your PS. That said, I did that. I had very bad grades and was on academic suspension. I came back, didn't get another B, and got my Master's . And that's what I wrote. I only got one interview, but I had had real jobs, so an interview I could do, and all I needed was one. Long story short, no excuses. If you want to talk about why, it had better be in the context of what you changed to be better. Excuses (hard classes, unfair profs, that kind if thing) will only hurt you. It sounds like at least part of your issues were unavoidable, but you still need to show that you have a plan to avoid academic failure in the future.