Overheating problems

This is my first build, and it isn't going to well. When I power on my computer, maybe half an hour later, it shuts off by itself. I realized it was overheating, so I left one side of my case open. Since now it's summer, even that won't help it from shutting off by itself. The only way I can prevent it from not shutting down is by using a window fan to blow into my open case. Besides that, I've added a hard drive fan, but still doesn't keep it from shutting off. My CPU (Q6600) temperature reads in the mid-50s when idle with the stock cooler, so yeah that's another problem, but i doubt that powers off my computer. I'm using a Raidmax Smilodon case and I've heard it was bad airflow. I have 4 case fans now (3 that came with the case and 1 hard drive fan I bought), and still doesn't prevent it from shutting off. Is there a way of fixing this overheating problem, that I don't have to leave my case open and use a window fan to blow air into the case?

EDIT: I finally got the Zalman 9700 on my Smilodon case (had to install it from the side of the case on the ground). My CPU temperature didn't drop as much as I expected it to be (it's around 40). Here are the current temperature I have (using Everest):

Motherboard: 22
CPU: 41
Core 1: 46
Core 2: 47
Core 3: 40
Core 4: 44
GPU: 54
GPU Ambient: 45
GPU Memory: 46

CPU voltage: 1.1

Now I just hope that my computer doesn't shut off by itself again.

re seat the heat sink... if its on in the wrong direction it might do that... it did that for me... turned sink 90 degrees and WALAH it worked

Is a new CPU cooler necessary? I know my temps are high, but would temps in the 50s really cause my computer to shut off by itself? I would get a new CPU, but all the decent ones don't seem to fit inside my case, I mean I had to rearrange my PSU wires a lot to fit even my stock cooler.

I actually do have a Zalman 9700 LED cooler, but it's just too big. I thought mounting it was hard enough, but when I actually get it to fit into my case, the wires of my PSU keep touching it. Some of the find on the cooler bent because of that. If I really tried, I could maybe get to fit in the case with all the wires, but I'm not really convinced that it's my CPU that's shutting off my computer, so I might just return it to Newegg. Right now I'm leaving one side of my case open, and it seems to work, but I know I need a better solution.

Yeah, I realized not there was 1 push pin that wasn't all the way in, but it wouldn't budge in. I just installed the Zalman 9700 cooler, and my temps still seem a bit high, around the low 40s idle. I've tried to tighten the screws as much as possible.

Here are current temps I'm reading from Everest:

Motherboard: 22
CPU: 41
Core 1: 46
Core 2: 47
Core 3: 40
Core 4: 44
GPU: 54
GPU Ambient: 45
GPU Memory: 46

CPU voltage: 1.1

Now I just hope that my computer doesn't shut off by itself again.

Heh... I just got my system OC to its max (3375mhz, on NV 650i), with a Q6600.

My vcore is 1.376 idle, on load 1.448.

Ambient temps yesterday in my room, 84F.

Under load:

Tcase - 64C max

Right now my Ambient temps are same 82F atm and my idle temp is 33C.

So something is up with airflow/HS.

I'm running 32-34 idle on my Q6600. That's with a lapped, Noctua (NH-12U??) and two 120mm fans in a push/pull configuration.
I might be tempted to lap the base of that cooler, and make sure you have enough Thermal Interface Material. Probably better to have just a bit too much than not enough.