Its says :

A problem has been detected and windows has been shut down to prevent damage to your computer.
If this is the first time you’ve seen this stop error screen,restart your computer.If this screen appears again, follow these steps: Run a system diagnostic utility supplied by your hardware manufacturer. In particular , rune a memory check, and check for fault your mismatched memory. Try changing video adapters.
Disable or remove and newly installed hardware and drivers.Disable or remove and newly installed software.If you need safe mode to remove of disable components,restart your computer,press f8 to select advanced start up options,and then select safemode.
Technical information: ***Stop:0x0000007f(00000008,0×80042000,0…
beginning dump of physical memory

Error code: 0x0000007F

Instructions: Run a system diagnostic utility supplied by your hardware manufacturer. In particular, run a memory check, and check for faulty or mismatched memory. Try changing video adapters.
Disable or remove any newly installed hardware and drivers. Disable or remove any newly installed software.

What does this mean!? Help please!!

I've been getting a blue screen with the following message: Run a system diagnostic utility supplied by your

Try changing video adapters. Disable and remove any newly installed hardware and drivers.
Disable and remove any newly installed software.

What does all this mean?

My computer has been very slow lately and I ran disk clean up and did defragmentation yesterday. However, I'm still getting blue screens.

How can I fix my computer? Would you please describe step by step the whole process.
Thanks.

P.S. I have a Dell computer, a windows xp