You could uninstall the Radeon drivers from device manager, remove Catalyst software, reseat the card, then use DriverCleaner in safe mode to remove remnants of past drivers and install fresh drivers. If that doesn't work you could reinstall Windows.

 

The problems you describe sound as if they could be hardware-related, so you should try the Radeon in another PC with an AGP slot and see if the same issues manifest. It is also possible the card is overheating, as my Radeon 9800 pro had a fan that went bad after a couple years causing artifacting. Use EVEREST Home Edition or some other monitoring software to check the temp of the core and see if its in the 80s or 90s Celsius, assuming the card has a sensor. Also try cleaning the Radeon's fan with compressed air and then unplugging it and replugging it to the card itself.

 

It's also possible your computer's woes are entirely unrelated to the video card itself. That memory error you mentioned and your virtual memory problems suggest your RAM is bad. Try MemTest86 (preferably on boot) to see if your memory has any errors. Otherwise there could be a physical problem with your motherboard itself.

Many thanks.  I will try these, starting with the fan, as today it is not sounding smooth. 

 

Yesterday the vertical bands disappeared after 20 minutes and the screen was clear for 12 hours until shut down, but they are back today. When on the internet, they are clearly a low res version of the current web page.  Dell tech support are insisting that I need a new graphics card, but also say that the Radeon 9800 is no longer available, and that the only one suitable is a slightly lower spec Nvidia.  We need to upgrade rather than downgrade, but cannot do this - computer is five years old and therefore apparently not capable of supporting current graphics cards. 

 

If I do have to replace the graphics card, I am really stuck with the Nvidia?  Currently have Ati radeon 9800 agp  256 Mb (installed as two 128mbs - why was it done this way?).

Unless your system is still under warranty you shouldn't rely on Dell for video card replacement because their upgrade process, from my experience, has limited selections with exorbitant pricing.

 

If your 9800 turns out to be dead I would recommend the 7600gt AGP.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814130099

It is tough to find that card in stock nowadays, but it is very fast compared to your 9800 agp. Your frame rates in games should double at the minimum. It is a mid-range card by modern standards so don't expect to play brand new games at good frame rates, but it is still quite competitive. For example, HL2: EP2 should run very nicely with that card. If you do get the 7600gt make sure to clean out your old ATI drivers with DriverCleaner before installing NVIDIA drivers.

 

That 7600gt should fit in your AGP slot and work fine with your 250w power supply. You will need two free molex connectors.

That sounds like a good option for replacement. I am concerned though about the way the 256Mb Radeon is installed as two x 128Mb, with separate memory allocations showing when I look at system - hardware -devices.  One of these has a list of memory addresses and an IRQ allocation. The other only has two memory address ranges (I thought it originally had more).

 

What is it about my system that made this necessary, and will a different card just install easily? Dell were insistent that there is only one other card that can be installed, ie the nvidia gforce fx 5200. Or do they mean that it is the only alternative that they sell?

 

 

I have an old Dimension 8300 that came with a 128MB Radeon 9800 pro. I had the exact same thing with memory addresses. In device manager, two video cards show up for some reason. I have no idea why but it shouldn't be a problem for a new card, as long as you uninstall the Radeon drivers.

 

When Dell says the 5200 is the only part you can get, they are just saying that because its the only one they sell, or it is the only other one that's "officially" supported. But your PSU has more than enough amps to juice the 7600gt, and the AGP slot is compatible.

 

Search the forums for "4600 7600gt" to read about other users who've had no problems running that card on the 4600.