My Dell i620 desktop is freezing up... Need help

[limewire]

So I bought a new desktop computer about 2 weeks ago and ever since I got it, it's been freezing (locking) up on me at random times. I currently use Windows 7 64-bit. I put in a new graphics card and new memory sticks just the other day and I got the same freezing problem. It's very random. I can be surfing the web and the next thing you know, the whole thing freezes up. I can't move the mouse. Can't do CTRL ALT DEL. Can't do anything. Seems as if the whole computer locks up. The only way to restart the computer is by manually holding in the power button for a few seconds. So since I replaced graphics card and installed new memory, I was thinking it may be something else causing this... Any suggestions on what might be the root cause of this disturbing issue?

 

[Raiddinn]

Try putting the old stuff back in and see if it works.

My guess is that it will and one of the following is true:
1) Bad new RAM
2) Bad new video card
3) Old PSU can't handle new video card
4) Two from above.
5) 1, 2, and 3.

It would be nice if you could respond with the part numbers of all of your parts so I can advise better about which one is the cause.

 

[limewire]

Try putting the old stuff back in and see if it works.

My guess is that it will and one of the following is true:
1) Bad new RAM
2) Bad new video card
3) Old PSU can't handle new video card
4) Two from above.
5) 1, 2, and 3.

It would be nice if you could respond with the part numbers of all of your parts so I can advise better about which one is the cause.

Ok... what are the chances the original ram and video card were bad as well. What I'm trying to say here is, I had the same issues even before the upgrades took place. It was completely stock when I first noticed it.

 

[Raiddinn]

Sorry, I must have misread something then.

Lets start over.

What are the maker and models of each of these parts (feel free to put them in a nice bullet point list like this, it makes for easier reading):
1) Motherboard
2) Processor
3) Old RAM
4) Old Video Card
5) Hard Drive
6) PSU
7) New RAM
8) New Video Card
9) Case

Additionally, I would like you to download and keep running a program called HWMonitor made by CPUID. Monitor it periodically for changes.

Also, before you go away from the computer for an extended amount of time, say sleeping, DL a program called MemTest86+, copy it on a CD, and boot with it in the drive and let it do this while you are away.