You mean, a positive HPT followed by a negative one? Or, just a negative HPT during early pregnancy before positive? This is very common especially if HPT was taken before a missed period. Most tests that I have seen say that on the day of or after the missed period, 95% of pg women get a positive. It is possible that your test isn't as sensitive or you are among the remaining 5%!
Sayoni, If you mean a negative test on a HPT ONLY, then.. it is either yo need to wait for some more time or your Hcg is too low to be detected on the HPT.. If you have skipped your periods way to far, I suggest you get a blood test. Now, THAT is accurate !! Best Luck !