What is the name of your state (only U.S. law)?
Pennsylvania.
Are dividends taxable if the principal is the same as the original investment at year end?
It's not clear what happened but let me give you one example of how that can work.
If you bought $10,000 worth of stock at the beginning of the year and were paid $1000 in dividends during the year the dividends would be taxable.
If the value of the stock dropped to $9000 by the end of the year your account would still be valued at $10,000 but you would still pay the tax on the dividends unless you sold the stock at a loss before the end of the year.
Then you could write off the capital loss of $1000 against the earnings of $1000 and pay no tax.
Now you can explain your situation.