C000021A & STOP: all errors .for xp professional.(it is all winlogon troubles of game or any program) dont delete winlogon.exe !!!! or any system file without read perfectly.dont install any exe or .reg .bat file . 1-first chek this address.you must search about reg edit fix reg edit repair .default regedit. http://support.microsoft.com/kb/156669/tr --- you search your language in support microsoft. http://www.kellys-korner-xp.com/xp.htm -----search registry files. http://www.exterminate-it.com/malpedia/remove-mssmgr check your hijack log. 2- install to that security programs same time . install this and update or buy .AVG internet security v.9.0801 . install other registiry celaner v.3.0.1 chek update . install junkfiles monitor v1.0 and (open auto strat check) install this advanced system care pro v.3.5.0 buy or update. install iobit security360 (open auto start all installed programs.) when your all installation is finish .same time you start this all programs .scan and clean scan and clean evry time every day .your xp system will be turn your default registry systems .by time and bye scan and clean.3 days you make update all programs. if you have any error lockable files or programs you install perfect uninstaller or final uninstaller. advanced system care pro will show to your monitor same error file .when you see same error file is in your system .update again all security programs .you start all security programs start on the desktop and scan errors. iobit securty will be redefault your system by time . adavnced stystem care and AVG internet securty when show to you green message system is cleen or secure . start +close computer +close when you see blue monitor C000021A & STOP DONT CLOSE SWİTCH OFF POWER .YOU TAKE OUT YOUR ELECTRYCITY CABLE SOCKET.AND START YOUR COMPUTER .İT WİLL BE OKaY .