This seems like there may be a problem with a script that you are trying to run, or the webserver is just not configured properly. Are you testing a php page that has code on it? You may need to enable error reporting, I'm not too familiar with XAMP but I imagine that there is either an interface or settings file you can adjust for this.
If the problem is just that the web server is not configured or running properly you should try to see if there is a full uninstall as just re-installing could potentially cause problems.