BIOS memory problem - help me!

OK, I have been having problems with my computer, which is a Dimension 2400. I got the error message, which in the form of a blue screen. This is exacly what it says - down to the last word.

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A problem has been detected and Windows has been shutdown to prevent damage to your computer.

IRQL_NOT_LESS_OR_EQUAL

If this is the first time you've seen this stop error screen, restart your computer. If this screen appears again, follow these steps.

Check to make sure any new hardware or software is properly installed. If this is a new installation, ask your hardware or software manufacturer for any Windows updates you might need.

If you problems continue, disable or remove any newly installed hardware or software. Disable BIOS memory options such as caching or shadowing. If you need to use Safe Mode to disable components, restart your computer, press F8 to select Advanced Startup Options, and then select Safe Mode.

Technical Information:

*** STOP: 0x0000000A (0x8066100F, 0x00000000, 0x8066100F)

Beginning dump of physical memory
Physical memory dump complete.
Contact your system administrator or technical support group for further assistance.

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Can you please help me? I suspect that I need to get a $70 replacement memory stick. But how do open a Dimension 2400? I tried, I looked on the back but no visible screws that hold the cover. I did this because I wanted to try to dust out the computer. There was a show or something I saw that it was a good idea to do this every once and awhile, and improve the performance a bit.