We searched for the standard model Higgs boson in many different channels using approximately 5 fb-1 of 7 TeV pp collisions data collected with the CMS detector at LHC. Combining the results of the different searches we exclude at 95% confidence level a standard model Higgs boson with mass between 127.5 and 600 GeV. The expected 95% confidence level exclusion if the Higgs boson is not present is from 114.5 and 543 GeV. The observed exclusion is weaker than expected at low mass because of some excess that is observed below about 128 GeV. The most significant excess is found at 125 GeV with a local significance of 2.8 sigma. It has a global significance of 0.8 sigma when evaluated in the full search range and of 2.1 sigma when evaluated in the range 110-145 GeV. The excess is consistent both with background fluctuation and a standard model Higgs boson with mass of about 125 GeV, and more data are needed to investigate its origin.