BSOD Multiple Instances/Possible Causes

I have a Dell Inspiron, 64 bit, that runs on Windows 7. Forgive me if I put a n00bish post, but I am at the end of my rope here. I wanted to try and fix it myself before coming here but I'm desperate.

Sometime in November, my computer bluescreened out of the blue. I didn't think much of it at the time. First of all, I baby my laptop, never install anything I'm not sure about, and I never go to sites if I'm not 100% confident in them. However, the shut downs started becoming more frequent, like once every three days. Then I started getting worried and rushed to start backing things up. Over time, I have discovered the following patterns:

1. It bluescreens whenever it is idle for more than 30 minutes
2. bluescreens after running for three hours
3. Bluescreens whenever I use windows to create a system back up. It won't even let me create my own system restore points anymore
4. bluescreens whenever I install ANYTHING
5. bluescreens whenever I try to update

Naturally I've tried doing virus scans. Got nothing. I tried repairing the disk. That went fine. I did a memory check, it says that the memory is good. I did a defrag, but it only made it through 80% before BSODing. And I did a system restore to the point before it started BSODing. No luck. All the drivers say they are up to date, as well.

Here's the thing, I NEVER do windows updates. I honestly don't trust them because windows updates have killed my last two laptops. But of course now that I actually try to install any of them, I get a BSOD.

I tried reading the .dmp files, but I get a bunch of gibberish and I can't install anything that would help me read them. So...help? D:

Thanks in advance!

Thank you! Okay, here we go.

Spybot Search and Destroy

Thank you so much! So far it's been running for 2.5 hours and has found 34 viruses. I'm on the edge of my seat hoping that the computer will stay on for the rest of the scan.

I feel kinda silly now. It never registered to me that anti-spyware was not the same as anti-virus.

I will keep you updated after I finish following the rest of your steps. Thank you so much for your help again. If this works, you're my new best friend.

It worked! Omigosh, thank you so much! I was able to install the Security Essentials and even update Java so I can play minecraft! Thank you thank you thank you! You seriously saved my livelihood! <3