When booting my MacBook, a question mark with folder appears

At first, I hit my macbook on the right side of the laptop, which froze it. I shut it down and restarted it only to find out that a folder with a question mark was blinking.

I took my macbook to an authorized apple store to get an estimate, and they said that my hard drive crashed and I needed a new one. It was too expensive to fix there so I took it back.

I then purchased my own hard drive, followed the instructions online, and installed it myself. I found my Snow Leopard OS installation CD and tried to reboot my computer. The folder came up again so I shut it down and restarted it then pressed Alt/Option.

I then clicked the install button and after a while, the computer would shut down itself.

After continuously trying to do this, I looked up some other alternatives and when restarting it, pressed Command + Alt/Option + P + R to restart the P RAM.

Still after a while, nothing. I didn't know what else to click so I went back to the hardware, took the hard drive and RAM's out and put them back in firmly.

Still, I had no luck. My computer is trying to reboot the system again but I don't know if it works. I don't know what else to do except to wait for now. If it starts working I'll update this, otherwise, I do not know what else to do!

Anyone with any suggestions please help! I would greatly appreciate it.