Once a request (Dispute) is closed it can not be re-opened.
On the other hand, you may still be able to get your money back. If your Paypal purchase was funded with a credit card.
Go to the credit card you actually paid with. Paypal is just a mediator. Phone the 1-800 customer service number and ask about a charge-back. While cc's have longer deadlines, they do have them. So act immediately. The clerk will need dates, payments, currency, transaction numbers etc, to process your refund.