Advice needed on how to get into a new industry.

So, I'm trying to determine how to get myself a job in an office. Be it an admin assistant, a secretary, a personal assistant even. I can't seem to break through though. My experience is in retail with a bit of a focus on inventory control. There's a couple gaps in my resume due to family health issues I was needed to help handle, so I don't know how to appropriately explain those on my resume and not look like a flake for not working for 2 separate periods of about a year. I'm 27 and trying to find a long term career instead of destroying my damaged back in retail forever. I know I can DO the tasks an admin assistant does, because I've already done them in some capacity for another job or for volunteer work, ect. I just have no idea how to really prove to someone that I'm capable on 2 pages of resume without actually talking to anyone.

Any ideas or advice anyone can give would be awesome, I'm in a bit of a pickle I guess and I really need to find something soon.