Does anyone know why this happens?

I don't know why it happens, but if it is helpful this happened to me with with my 5870 Catalyst 9.11 when my memory overclock wasn't stable.

Maybe you should upgrade your power supply.

Yeah, a 250w PSU these days is probably insufficient, especially if you have a decent graphics card that gets a bit of a workout, as yours obviously does.  A PSU upgrade is probably in order... but there has been some comment regarding recent Nvidia drivers not being the best, so checking for and installing a stable release might help, if that's the case.

Best of luck with it.

YOu do need a new psu.   They're isnt enough power to run everything and refresh the dram on the card giving you the memory errors

Actually, I just resolved this same problem just days ago...

One small difference is that my Video Card is an ATI 5850.

I put together a new theme for my desktop from various downloads here at wincustomize, but this time I felt like I wanted to base my theme aroud a Dream.  I went with "Red Giant" by Master Baron, a beautiful Dream. 

I worked out the whole entire theme... Windowblind, Icons, Cursor, Docks, Widgets and so on.

Shortly there after... I started getting the same problem you are having.

I quickly figured out that the problem was due to the Dream I was running.

I think that it is a problem with the TYPE of Dream or a compatability problem with Windows 7, I'm not sure.

I know it's not a problem with my rig, as everything else runs super fine with Core I7 920, 128Gb SSD, 6Gb ddr3-tri channel ram, 1000 watt PS, and so on.

So the big question to you... Are you running a Dream?

Looks like I found a new home for this brand new 400 watt PSU I have sitting here taking up space.

Thanks for the input guys. After the RAM upgrade,CPU upgrade and GFX card I suspected the power supply just wasn't up to the task.  I hope this takes care of it.

I agree 100% but will add that I was running ok with the drivers Windows 7 found for my Nvidia but I went to the web site and downloaded the latest ones for my card and it runs like a top now. You may need to do both things as Starkers suggested.

Link for drivers  http://www.nvidia.com/Download/index.aspx?lang=en-us

If the card requires 300 and you've only got 250, you should probably get 400, at least.

I'm sorry, this question kinda feels like asking why the air condition doesn't work in my car - I mean, sure, I've got a huge hole in my roof, but surely it can't be the issue?

New PSU. Get one.

Edit: 196.21 are the latest ones, since they apparently discovered a problem with the previously latest ones. I even had to downgrade, so yeah, I remember that.

Make sure you are not using the Nvidia driver described here in this Maximum PC LINK

No.  But thanks Narbytrout.

Thanks Wiz. You're a real friend! 

Just crashed again....here is what I got from Administrative Events:

Log Name:      System
Source:        Microsoft-Windows-Kernel-Power
Date:          3/25/2010 10:15:01 PM
Event ID:      41
Task Category: (63)
Level:         Critical
Keywords:      (2)
User:          SYSTEM
Computer:      JimDillard-7
Description:
The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Kernel-Power" Guid="{331C3B3A-2005-44C2-AC5E-77220C37D6B4}" />
    <EventID>41</EventID>
    <Version>2</Version>
    <Level>1</Level>
    <Task>63</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8000000000000002</Keywords>
    <TimeCreated SystemTime="2010-03-26T02:15:01.917600000Z" />
    <EventRecordID>85204</EventRecordID>
    <Correlation />
    <Execution ProcessID="4" ThreadID="8" />
    <Channel>System</Channel>
    <Computer>JimDillard-7</Computer>
    <Security UserID="S-1-5-18" />
  </System>
  <EventData>
    <Data Name="BugcheckCode">0</Data>
    <Data Name="BugcheckParameter1">0x0</Data>
    <Data Name="BugcheckParameter2">0x0</Data>
    <Data Name="BugcheckParameter3">0x0</Data>
    <Data Name="BugcheckParameter4">0x0</Data>
    <Data Name="SleepInProgress">false</Data>
    <Data Name="PowerButtonTimestamp">0</Data>
  </EventData>
</Event>

Where is Yrag?

Have you ever tried to overclock you pc?  If so, try using all of the default setting on your voltages.  If you have not ever overclocked your pc try raising your MCP, FSB, and RAM voltages "one notch".

Another thing to try is disabling the "IPHelper" service by going into System and Security - Administrative tools - Services.  While you are inside the services page there are other unnecessary programs you can disable or set to manual - here is a LINK to a very simple guide to follow.

Yet another thing to check is... Is your power management (sleep, hibernation, etc.). If you need to manually re-enable hibernation do this:

1) Run the command prompt as administrator (it's under Accessories, right click and "Run as Administator".

2) Type the following: power -h on.

I hope this helps, I know how much of a pain it is to agonize over these issues for nights on end.

I fail to understand how enabling hibernation can help here.....am I missing something?

I don't overclock anything, and don't think it's a good idea.  

Also, I must say, Wiz's gift of a 400W PSU did increase my WEI score, I still crashed after that, so I am still looking for other causes/solutions.

This happened to me a bunch on my old laptop, and after a couple of weeks with sporadic crashing it died. I took it to microcenter and they replaced the motherboard, and it worked for another two months before dying again.

Sorry, not helpful, but be careful. Hope it works out for you.

Same here. The video card on my laptop overheated and fried the motherboard in the process, thanks to some poor designs on HP's and Nvidia's parts. I had about 2 weeks of this error, then it died completely.

So good luck. I hope you don't have the same problem I had, and you can get it figured out.

Might be the nVidia drivers Jim, my son was using my XP system to play a game today and the video drivers crashed too with the same type of error.  First time it has ever done that. looks like nVidia put out updated drivers yesterday, downloading them now.

Me too! Thanks Tom!!!!

I'll get work on Aztec.

Mine used to crash with Dreams on a nvidia card but since updating my card, my crashes have stopped.

Drives.

I had the same thing with my nVidia. It took about 2 months for an update to them to be published and it stopped.

OK, SO FAR, I haven't crashed. I updated the video driver, nVidia has a new one, I updated my power supply, and Wiz and I have been on Yahoo Video chat all night, and I had photoshop open all the while. SKS7 open too. And skype.

Probably unrelated, I found that windows update had given me nVidia sound drivers, when I also had realtek installed, which is the correct driver. Dunno why W.U. would put nVidia sound drivers on my system. But I'm sure there was a conflict there somewhere.

Anyway, so far, so good......  

nVidia sound drivers???  I did not even know they made a sound card. 

If it has HDMI hook up then it installed the HDMI audio drivers. The nVidia card I installed on my step-sons PC did the same thing only he lost all sound until I figured it out.