Just to make sure it's not a memory hardware problem, download a copy of Memtest86 from here, burn it as an image to a CD, and boot it.  It's a small utility that exercises memory looking for problems.  If it finds one, you know what the problem is.  If it doesn't that's one thing to eliminate.  Let it run for a couple of hours.

If there are no memory errors, you might try using the driver verifier function of WhoCrashed.  It might point you to the driver.

As a last shot, the errors you were seeing may not have been with just the video card.  It may have also corrupted your Windows installation.  It's a big step but you might try re-installing Windows from the CDs or restore partition.  Make sure you have your data and configuration backed up and have all your software distributions and license keys before you begin.

A couple of things to try.  See what happens as you work through the options.

There is no way to change the memory timings - there simply are no such BIOS settings. 

Hi 

Thanks for the info.

I've already reinstalled windows plenty of times, I've ran the full system diagnostic tests and memtest86+ and all showing no problems.

I've asked some guys at sevenforums and showed them my dmp files, CPU-Z screenshots, RAMmon reports and then they pointed out that my ram timings are wrong and that I need to change them (i.e. theres nothing actually wrong with the hardware itself) .

However I'm struggling to do that as the BIOS interface is extremely limited (there's no bloody way to change ANYTHING AT ALL - apart from the time and date and a few security settings). 

When I had a replacement motherboard, the tech guy messed around and managed to change the service tag on the BIOS, maybe there's a way to get to the "advanced" bios settings? 

There's not really any memory settings on the laptop.  Changing the service tag is unrelated.  The BIOS will detect the memory timings and set them when you plug in the memory chips.  If the tech didn't do it when he swapped out the motherboard, you might try reseting the BIOS settings to factory defaults and see if that changes anything.  Write down all the settings before you do though. 

If you've got any ATI drivers loaded, you might want to play around with the settings.  Try turning off hardware acceleration on the video driver.

Unless you can get more information on the crash, it's going to be difficult to figure out which driver is causing this.

Here's all the information about the crash dumps, drivers, pc info, etc etc

http://dl.dropbox.com/u/8250337/Seven%20Forums.rar

Things I see right off the bat.

• You've got the latest ATI driver loaded for the 5400.  Turn off hardware acceleration and see if it still crashes.
• There appears to be drivers for the Brother MFC printer driver loaded.  They're from 2006 so I'm not sure if they are current.  Can you go out to the website and see if there are later versions of the drivers or if you don't use that printer any more, uninstall the software?
• It's not a big deal but the System Event Log only goes up to 02-23-2011 but the dumps are from the 25th on.
• Did you install anything just prior to when the BSODs started happening?  Possibly the ATI driver.
• I saw an old copy of SYSTOOLS driver loaded.  I assume you're not tweaking the timings, right?  Also the driver was from 2006.  Can you either uninstall or update that too?

I don't mean to pick on the ATI driver but I've already been burned by the latest drivers.  I had to revert to a driver version closer to when the motherboard came out.  I think it was around November of last year.  ATI has suffered with stability issues with the drivers over the years.  They may not be the culprit but just a suspect.  You might try the version from Dell and see if it's any better.

Try one thing at a time and run the system to see if that was it.  If you change everything at once, you'll never know what the problem was.

Here's some new event logs and a new crash dump from last night:

http://dl.dropbox.com/u/8250337/New%20info.rar