Your equity in the partnership determines whether you can deduct losses from your income.
As @M-MTax said if Box L of your Form K1 shows your Capital account balance i.e. your equity in the partnership.
If you have a $0 or less balance in your Capital account at year end, you are not allowed to deduct a loss as you no longer have any equity in the partnership. You in essence no longer have any at risk investment to write off.
Form K1 (1065)
