Win2K-The memory could not be read.

Hi there,
I hope I am in the right group. I apologize if there are something
wrong
My computer always hang on or errors prompt out every time when I open
any application.
The instruction at "0x01fd80ca" referenced memory at "0x00000004". The
memory could not be read.
I am using Windows 2000 service pack 3. Can anyone tell me what is the
problem of my PC and how can I fix it?
Waiting for your answer.
Thanks a lot.
Hung