I am going to be a little bit negative here.
Anyone who ask "I need ideas to start a business" is not ready to start a business. You need to have ideas first, then pursue it as a business.
Why? Because if you have to get ideas from other people, you are simply not going to be competitive. Whatever business you enter into, you are no better than the next person going into the same business. It probably doesn`t require special skills (administrative background is not a special skill), so anyone can get in. Most likely, you will end up competing on price and work long hours to make the end`s meat. That`s not the way to create a successful business (or even a successful self-employment job).
This is simply how free market works. When a product or service can be offered by anyone, it is a commodity, and it always end up being a low margin thing.
You have to dig deeper to find something right for you. "Administrative background" is just a start. You have to find something which differentiate yourself more.
Let me give you an example - if you have been doing administrative work for a particular industry, that will be a great asset and not everyone can do it. Let me be even more concrete - if you have done import/export administrative work, you can easily do an import and export consulting business, because that is foreign to most people.
That was just an example. You need to think about your past experience and think hard about what make youself different. A lot of things may be so natural to you that you don`t even see it, but may be very valuable to others.