I am a new realtor, and had no income last year. I am being prompted to enter income before my home office deduction and expenses will calculate, but had no income.

Did you input anything into the income field, even if it was a 0?  If not, you may need to try that.  If you did that and it did not work, maybe put it in a $0.01

That is correct. You can't take a home office deduction with no income. While you may be able to take other expenses, you can't deduct a home office without positive income.

The additional expenses I've entered don't seem to have an effect either.  Does that sound right?

The home office expenses would not be allowed in the current year unless you had income to absorb them. However, they would be carried over to the next year to be applied against next year's income.

Also, expenses you had before you were open for business would be considered start-up expenses that should be deducted in the first year you are open for business, even if incurred during the year before.

So, if you are new to the real estate business, expenses you had before you got your license and started to market homes would be start-up expenses that you should wait and record as such next year.