Windows se ferme à heure fixe (12:15)

Bonjour,
Il m'arrive qqch de très bizarre mon windows XP se met à fermer toutes les fenêtres pour finalement s'éteindre tout seul. J'ai installé Windows 7 : même problème au bout de plusieurs jours de fonctionnement....
Voici, un extrait de HiJackThis, si qqun a une idée:
Logfile of Trend Micro HijackThis v2.0.2
Scan saved at 21:23:54, on 25/07/2009
Platform: Unknown Windows (WinNT 6.01.3004)
MSIE: Internet Explorer v8.00 (8.00.7100.0000)
Boot mode: Normal

Running processes:
C:\Windows\system32\taskhost.exe
C:\Windows\system32\Dwm.exe
C:\Windows\Explorer.EXE
C:\Windows\System32\CtHelper.exe
D:\- = = U T I L I T A I R E S = = -\uTorrent\uTorrent.exe
C:\Windows\system32\mmc.exe
D:\- = = I N T E R N E T = = -\Firefox\firefox.exe
I:\DVD_Compilation_3\SOFT ADvanCED OS\ProcessExplorer\procexp.exe
D:\- = = P L A Y E R = = -\Winamp\winamp.exe
C:\Program Files\Trend Micro\HijackThis\HijackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = https://www.bing.com/?toHttps=1&redig=5FC791212101479BAFBE1A679848B1AF
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = https://www.msn.com/fr-fr/?ocid=iehp
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 - HKLM\Software\Microsoft\Internet Explorer\Search,SearchAssistant =
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,CustomizeSearch =
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName =
O4 - HKLM\..\Run: [CTHelper] CTHELPER.EXE
O4 - HKLM\..\Run: [CTxfiHlp] CTXFIHLP.EXE
O4 - HKLM\..\Run: [WinampAgent] "D:\- = = P L A Y E R = = -\Winamp\winampa.exe"
O4 - HKLM\..\Run: [Ad-Watch] C:\Program Files\Lavasoft\Ad-Aware\AAWTray.exe
O4 - HKLM\..\Run: [LogMeIn GUI] "C:\Program Files\LogMeIn\x86\LogMeInSystray.exe"
O4 - HKCU\..\Run: [uTorrent] "D:\- = = U T I L I T A I R E S = = -\uTorrent\uTorrent.exe"
O4 - HKUS\S-1-5-19\..\Run: [Sidebar] %ProgramFiles%\Windows Sidebar\Sidebar.exe /autoRun (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-19\..\RunOnce: [mctadmin] C:\Windows\System32\mctadmin.exe (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-20\..\Run: [Sidebar] %ProgramFiles%\Windows Sidebar\Sidebar.exe /autoRun (User 'NETWORK SERVICE')
O4 - HKUS\S-1-5-20\..\RunOnce: [mctadmin] C:\Windows\System32\mctadmin.exe (User 'NETWORK SERVICE')
O4 - HKUS\S-1-5-18\..\Run: [DevconDefaultDB] C:\Windows\system32\READREG /SILENT /FAIL=1 (User 'SYSTEM')
O4 - HKUS\.DEFAULT\..\Run: [DevconDefaultDB] C:\Windows\system32\READREG /SILENT /FAIL=1 (User 'Default user')
O13 - Gopher Prefix:
O16 - DPF: {D27CDB6E-AE6D-11CF-96B8-444553540000} (Shockwave Flash Object) - http://fpdownload2.macromedia.com/get/shockwave/cabs/flash/swflash.cab
O17 - HKLM\System\CCS\Services\Tcpip\..\{629F7C6F-025A-4A9E-A647-4D2B26251BEF}: NameServer = 212.27.54.252,212.27.53.252
O23 - Service: NVIDIA Display Driver Service (nvsvc) - NVIDIA Corporation - C:\Windows\system32\nvvsvc.exe