Pc starts but shuts down after few seconds without booting

Hey guys, so im new to your forum so forgive me for folish questions.
Some days ago I bought new parts to upgrade my pc
-mobo (msi B85M-E33)
-CPU(intel i5 4470)
-Ram(G-Skill 4gb 1600)
and a new cooler freeze 13
My HD is a seagate 500gb and i have a power supply of 550W
After replacing all the parts like always, when i start the pc it goes on but then it shutdown after few seconds and i dont see anything on the screen. i already cheked the ram and when its not plugged it does the beeps, but when i removed the cpu to check it doesnt do any beep without the cpu :confused:
Need some help!!!

Thanks