Windows XP Panda problem

When my computer is idle or left on for a period of time, once in a while I'll come back to a black screen(similar to dos) saying that it has shut down windows to protect it from harming the files, so when I restart it gives me the option to only start up in safe mode in which I have to install then reinstall Panda antivirus, I'm not sure how exactly this happens or if it is a regular happenstance of panda antivirus, but my home business is run thru my computer and sometimes when it's shut down it puts my files in jeapordy. I was just inquiring as to whether this is a problem, or what.....any feedback will be greatly appreciated, thank you