I installed raspberian in my raspberrypi. It worked for the first time. But when I shut it down, it didn't reboot again. So, I had to format the sdcard and reinstall the raspberian again. And unluckily this happens every time I shut the power down.
Try jumping GPIO PIN 5 to GND PIN with a bit of wire, only momentarily, you could use a switch in the future to make it easier. This should boot up the pi after shutdown.
If it powers up but doesn't boot into the OS, try reading the image in Win32DiskImager or similar and compare it to a fresh image that you know will work and see what's different or if the old one is corrupted.