A negative result can mean that you are not pregnant or that you took the test too early. Pregnancy tests vary in their sensitivity (how soon they can detect the hormone hCG), and you may not have given your body enough time to produce enough of the hCG hormone to show up on the test.
When taking a test it is best to follow the instructions of the manufacturer and wait until you have missed a period before taking the test. Some women show up accurately on a test the day they miss a period, while others may not show up positive until 3-4 weeks after a missed period. If the result is negative, wait a week and test again if a normal period has not started.