Can I receive a tax refund even if I haven't paid US tax?

In a few cases, yes. If you have children younger than 17 who are American citizens and have social security numbers, you could be eligible to receive the Additional Child Tax Credit. If you supported an American child attaining a bachelor's degree abroad or in the states, or if you yourself are enrolled in a qualifying degree program, you could be eligible for the American Opportunity Tax Credit.

UPDATE: April 2019 - The American Opportunity Credit will no longer be available to those attending foreign universities from tax year 2018 forward.