Win XP Pro Problem

Computer worked fine till now, sadly its probably something i downloaded. It will boot up al the way to the login screen. When at the login screen youll proceed to login and it will play half of the "windows starting up" chime stop. Youll see the desktop wallpaper for 5-10sec the computer will then click and restart or shutdown depending on what bios setting I have it on. I can start up windows in Safemode however. Any help whatsoever is greatful hopefully asap. If system specs and stuff are needed just let me know. Ty ^^


Edit: Turned off auto restart and got this error...

STOP: c000021a {Fatal System error} The windows logon process system process terminated unexpeectedly with a status of 0xc0000005 (0x00000000 0x00000000). The system has been shut down.