Computer freezes for no reason

Hello I am new here and I think I came to the right site for help. I searched and searched and couldn't find anyone with the specific problem I have. I have:
Windows 7 64 bit Ultimate
My pc manufacturer is Acer
Model Aspire M5200
Processor AMD Phenom 9950 Quad-Core Processor 4 CPUs ~2.2Hz
4096MB RAM Memory
Page File 1689MB used,6499MB available
Direct X 11

-Display Device-
NVDIA Geforce GTS 250
Manufacturer Nvidia
Chip Type Geforce GTS 250
DAC Type Integrated RAMDAC
Approx Total Memory 2797MB
Current Display Mode 1600 x 900 (32 bit) (60Hz)
Monitor Generic PnP Monitor

That info is from a 64 bit dxdiag.

The Problem: My computer freezes for no reason at all. Most of the time it's during firefox. Especially youtube. Sometimes the desktop. My computer freezes completely I tried everything to unfreeze it so I have to resort to holding the start button. And overtime it will destroy my computer if I keep doing it. I do not know what is causing it. I scanned with spybot and avg and both found no viruses. If I need to buy a new computer I cannot because I am still a child that cannot work and my parents are divorced and neither of them will buy me a new one. That also goes for repairs.
Any help is appreciated.
Thank you.

Things I have tried:
Running CCleaner
Scanning for viruses
Cleaning dust from inside of PC(There was only a bit)
Leaving side of computer open for the summer

In task manager processes it says physical memory at 38% is that bad? The CPU usage is not high either.

 

That sounds like the RAM Module, try to test your RAM or clean it with a rubber eraser.

If you don't know how to do that i will send you some pictures.

 

Yes I would like some pictures

 

[IMG=http://img822.imageshack.us/img822/628/finalsteps.th.jpg][/IMG]

http://img822.imageshack.us/img822/628/finalsteps.jpg

Look, you have to open your CPU, take care to don't dissconnect anything.

Look for your RAM Modules (maybe are two or three) quit them and clean the golden pins with the eraser slowly and carefully, the most important is don't touch the golden pins with your fingers.

Try to see how are the RAM Slots on the board, try to memorize that, will be usefull to put them again.

Now, you can test if one of these RAM Modules is not working propierly, so you could put just one and test if the computer frezees, if the computer frezees (quit that and put another) and test one by one after clean them all.

Other important thing is "If youren't sure to do this, then don't do it"

If just using one still the problem we will see what do.