While it is possible to take a deduction for depreciation on home computers used for investments, there is no way to modify this field within Federal Q&A.
You will need to manually calculate the depreciation and enter the amount as Other Expenses.
On the other hand, you can create a "dummy" Schedule C in the TaxAct program to calculate the depreciation amount, then delete that Schedule C. (You will need to be using the TaxAct Premium edition in order to create a Schedule C)