Can I file a 2007 federal income tax return if I had no income?

Yes, I'm asking because of the "refund." My only income per se for 2007, if it counts for any are my college loans/federal grants.

No. You need to get a W2 form anyway to be able to fill out your tax return. Besides, paying towards the government or loaning businesses isn't a job. Therefore, no tax paying.
In Canada you definitely want to because that's the only way you can get a GST rebate. Also if you're a student it's beneficial towards any grants, student loans, etc.
In order to file 2007 tax return to get benefits from the stimulus package, you have to have earned at least $3,000 and show it on your return as income.
If you have no income there is no need to file a tax return. Student loans and grants are not taxable income and are not listed on a tax return as income. Your college loans and grants are not qualifying income for the stimulus plan payments so if that's all of the "income" that you received you will not receive anything under the stimulus plan. All is not lost however. If you have at least $3,000 in qualifying income in 2008 you will receive your stimulus plan rebate when you file your 2008 tax return in 2009. So get yourself a job that pays you at least $3,000 in 2008 and you'll get it next year.
No, loans and grants aren't qualifying income for the rebate, so you aren't eligible. Trying to file a return won't change that.