Mon pc reboot de temps en temps au demarrage

Bonjour,
j'ai un sourcis avec mon pc.
Celui-ci reboot de temps en temps quand je l'allume et qu'il arrive a l'affichage de Bienvenue.
Et de temps en temps, il ne reboote pas. C'est alléatoire.

Je me demande pourquoi .

je donc le log :

Logfile of Trend Micro HijackThis v2.0.0 (BETA)
Scan saved at 20:57:13, on 28/07/2007
Platform: Windows XP SP2 (WinNT 5.01.2600)
Boot mode: Normal

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\winlogon.exe
C:\WINDOWS\system32\services.exe
C:\WINDOWS\system32\lsass.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\Program Files\Alwil Software\Avast4\aswUpdSv.exe
C:\Program Files\Alwil Software\Avast4\ashServ.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\igfxpers.exe
C:\Program Files\Intel Audio Studio\IntelAudioStudio.exe
C:\PROGRA~1\ALWILS~1\Avast4\ashDisp.exe
C:\Program Files\Spybot - Search & Destroy\TeaTimer.exe
C:\Program Files\Soft4Ever\looknstop\_looknstop.exe
C:\WINDOWS\system32\ctfmon.exe
C:\Program Files\No-IP\DUC20.exe
C:\WINDOWS\system32\spoolsv.exe
C:\Program Files\Intel\AMT\LMS.exe
C:\WINDOWS\system32\svchost.exe
C:\Program Files\RealVNC\VNC4\WinVNC4.exe
C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe
C:\Program Files\Alwil Software\Avast4\ashWebSv.exe
C:\WINDOWS\System32\svchost.exe
C:\Program Files\Mozilla Firefox\firefox.exe
C:\Documents and Settings\personnel\Bureau\HiJackThis_v2.exe

R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://go.microsoft.com/fwlink/?LinkId=69157
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://go.microsoft.com/fwlink/?LinkId=54896
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = https://www.bing.com/?toHttps=1&redig=5FC791212101479BAFBE1A679848B1AF
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = https://www.msn.com/fr-fr/?ocid=iehp
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Liens
O2 - BHO: Aide pour le lien d'Adobe PDF Reader - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Program Files\Fichiers communs\Adobe\Acrobat\ActiveX\AcroIEHelper.dll
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O4 - HKLM\..\Run: [IgfxTray] C:\WINDOWS\system32\igfxtray.exe
O4 - HKLM\..\Run: [Persistence] C:\WINDOWS\system32\igfxpers.exe
O4 - HKLM\..\Run: [SigmatelSysTrayApp] sttray.exe
O4 - HKLM\..\Run: [IntelAudioStudio] "C:\Program Files\Intel Audio Studio\IntelAudioStudio.exe" TRAY
O4 - HKLM\..\Run: [Look 'n' Stop] "C:\Program Files\Soft4Ever\looknstop\looknstop.exe" -auto
O4 - HKLM\..\Run: [avast!] C:\PROGRA~1\ALWILS~1\Avast4\ashDisp.exe
O4 - HKCU\..\Run: [SpybotSD TeaTimer] C:\Program Files\Spybot - Search & Destroy\TeaTimer.exe
O4 - HKCU\..\Run: [ctfmon.exe] C:\WINDOWS\system32\ctfmon.exe
O4 - Startup: No-IP DUC.lnk = C:\Program Files\No-IP\DUC20.exe
O4 - Global Startup: Adobe Reader Synchronizer.lnk = C:\Program Files\Adobe\Reader 8.0\Reader\AdobeCollabSync.exe
O4 - Global Startup: Lancement rapide d'Adobe Reader.lnk = C:\Program Files\Adobe\Reader 8.0\Reader\reader_sl.exe
O4 - Global Startup: Microsoft Office.lnk = C:\Program Files\Microsoft Office\Office\OSA9.EXE
O9 - Extra button: (no name) - {e2e2dd38-d088-4134-82b7-f2ba38496583} - %windir%\Network Diagnostic\xpnetdiag.exe (file missing)
O9 - Extra 'Tools' menuitem: @xpsp3res.dll,-20001 - {e2e2dd38-d088-4134-82b7-f2ba38496583} - %windir%\Network Diagnostic\xpnetdiag.exe (file missing)
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O16 - DPF: {6E32070A-766D-4EE6-879C-DC1FA91D2FC3} (MUWebControl Class) - http://update.microsoft.com/...
O20 - Winlogon Notify: Antiwpa - C:\WINDOWS\SYSTEM32\antiwpa.dll
O22 - SharedTaskScheduler: Pr-chargeur Browseui - {438755C2-A8BA-11D1-B96B-00A0C90312E1} - C:\WINDOWS\system32\browseui.dll
O22 - SharedTaskScheduler: Dmon de cache des catgories de composant - {8C7461EF-2B13-11d2-BE35-3078302C2030} - C:\WINDOWS\system32\browseui.dll
O23 - Service: avast! iAVS4 Control Service (aswUpdSv) - ALWIL Software - C:\Program Files\Alwil Software\Avast4\aswUpdSv.exe
O23 - Service: avast! Antivirus - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashServ.exe
O23 - Service: avast! Mail Scanner - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe
O23 - Service: avast! Web Scanner - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashWebSv.exe
O23 - Service: Service d'administration du Gestionnaire de disque logique (dmadmin) - Unknown owner - C:\WINDOWS\System32\dmadmin.exe
O23 - Service: Journal des vnements (Eventlog) - Unknown owner - C:\WINDOWS\system32\services.exe
O23 - Service: Service COM de gravage de CD IMAPI (ImapiService) - Unknown owner - C:\WINDOWS\system32\imapi.exe
O23 - Service: Intel(R) Active Management Technology LMS Service (LMS) - Intel - C:\Program Files\Intel\AMT\LMS.exe
O23 - Service: Partage de Bureau distance NetMeeting (mnmsrvc) - Unknown owner - C:\WINDOWS\system32\mnmsrvc.exe
O23 - Service: Plug-and-Play (PlugPlay) - Unknown owner - C:\WINDOWS\system32\services.exe
O23 - Service: Gestionnaire de session d'aide sur le Bureau distance (RDSessMgr) - Unknown owner - C:\WINDOWS\system32\sessmgr.exe
O23 - Service: Carte puce (SCardSvr) - Unknown owner - C:\WINDOWS\System32\SCardSvr.exe
O23 - Service: SecureStorageService - Unknown owner - C:\Program Files\Wave Systems Corp\Secure Storage Manager\SecureStorageService.exe (file missing)
O23 - Service: Journaux et alertes de performance (SysmonLog) - Unknown owner - C:\WINDOWS\system32\smlogsvc.exe
O23 - Service: Clich instantan de volume (VSS) - Unknown owner - C:\WINDOWS\System32\vssvc.exe
O23 - Service: VNC Server Version 4 (WinVNC4) - RealVNC Ltd. - C:\Program Files\RealVNC\VNC4\WinVNC4.exe
O23 - Service: Carte de performance WMI (WmiApSrv) - Unknown owner - C:\WINDOWS\system32\wbem\wmiapsrv.exe