Problem starting Autocad 2002 as a windows2000 administrator

Hi I wonder if any of you could help with a couple of problems I'm having when starting AutoCAD 2002. When I log on as an administrator in windows 2000, I get an error just when today starts to load. It says something like: The instruction at '' referenced memory at ''. The memory could not be read. Click OK to terminate the program. But when I log on as a power user it works fine, bar a message which comes up with a registry error. I don't really know what to do in these situations. I've tried re-installing it. I've checked which processes each are running, both exactly the same. I also checked the free memory virtual & physical, both roughly the same. Is there anything else I could try? Thanks in advance Rich