While your original intent was not to obtain an income - the fact of receiving an income is a taxable event.
If you do not rent your property to make a profit, you can deduct your rental expenses only up to the amount of your rental income. You cannot deduct a loss or carry forward to the next year any rental expenses that are more than your rental income for the year.
Where to report. Report your not-for-profit rental income on Form 1040 line 21. For example, if you are filing Form 1040, you can include your mortgage interest and any qualified mortgage insurance premiums (if you use the property as your main home or second home), real estate taxes, and casualty losses on the appropriate lines of Schedule A if you itemize your deductions.
Claim your other rental expenses, subject to the rules explained in chapter 1 of Publication 535 - www.irs.gov/pub/irs-pdf/p535.pdf , as miscellaneous itemized deductions on Schedule A (Form 1040), line 23. You can deduct these expenses only if they, together with certain other miscellaneous itemized deductions, total more than 2% of your adjusted gross income.
Information about Pennsylvania Property Tax/Rent Rebate may be found here - http://www.revenue.state.pa.us/portal/server.pt/community/property_tax_rent_rebate_program/11410
The deadline to apply for a rebate on property taxes or rent paid in 2009 is Dec. 31, 2010.
Let me know if you need any help.
According to the tax law - yes - you should amend all past returns - add all missing income and deductions, and pay any additional taxes.
Please consider that you will be liable for penalties and for interest because of late payments.
As a practical matter - please be aware that there is a general three year statute of limitation for the IRS to assess additional tax liability if you failed to report any taxable income.
I might suggest to discuss the issue with your tax prepare and estimate possible tax liability before stepping forward.