System error memory dump files

Have Dell Vostro 200 desktop. PC was very slow and stagnant so I decided to reinstall the operating system XP Svc pk 2. After the repair install the pc hangs on the windows loading black screen and will stay there. I then manually reboot and after reaching the login screen and choosing my password the screen either restarts, ask me to activate windows. After either screen it then goes into the system error and starts a memory dump.