If you only have one property there is no way on this green earth that you will ever convince the IRS that rental property is the absolute only thing you use that computer for. It's just not gonna happen. You and I both know it. So I recommend you not even go there. Besides, if you don't know it already, when it comes to taxes rental property "ALWAYS" operates at a loss. Especially if you have a mortgage on it. When you add up the depreciation you are required to take by law, along with the mortgage interest deduction, property tax deduction and property insurance deduction, those four deductions alone will exceed the total rental income you'll get for the property for the year. Add to that the other rental expenses such as repairs, maintenance, etc and you are guaranteed to never ever have a taxable profit with each passing year. You will have a cash flow. But you won't have a taxable profit.

So trying to claim the computer in any capacity, be it as an asset or an expense will not make one single penny of difference in your tax liability.  This is why I recommend you not waste the time and effort on this. It will all be for nothing in the end.