If the IRS adjusted your refund they will be mailing you a letter explaining why they changed it. It may have been offset for a debt you owe. Treasury Offset Program TOPS
http://fiscal.treasury.gov/fsservices/gov/debtColl/dms/top/debt_top.htm
I would check over your return and see if you can see anything wrong especially in the payments section. Make sure you agree with all the amounts listed. Like is the difference the same or close to the refund you got last year? Maybe you put down that you applied last year's refund to this year? Or you applied part of your refund to next year as an estimated payment. Or you put down you made a payment with an extension or paid an estimated payment that you didn't make?
Do you get Social Security? Is there an amount on 1040 line 6b or is it 0?
There is a new question this year asking if you lived in a foreign place. People have been answering it wrong or skipping it. Go back through the Social Security entries. And it is for each spouse. So if you have a low amount on 1040 line 6b you might have answered wrong for 1 person.
