Dopo varie scansioni e aggiornamenti vi mostro il nuovo log con hjt:
Logfile of Trend Micro HijackThis v2.0.4
Scan saved at 17:55:54, on 30/07/2011
Platform: Windows 7 (WinNT 6.00.3504)
MSIE: Internet Explorer v9.00 (9.00.8112.16421)
Boot mode: Normal

Running processes:
C:\Windows\system32\taskhost.exe
C:\Windows\system32\Dwm.exe
C:\Windows\Explorer.EXE
C:\Program Files\AVAST Software\Avast\AvastUI.exe
C:\Windows\system32\taskhost.exe
C:\Program Files\Mozilla Firefox\firefox.exe
C:\Program Files\Mozilla Firefox\plugin-container.exe
C:\Program Files\Mozilla Firefox\plugin-container.exe
C:\Program Files\Windows Mail\WinMail.exe
C:\Program Files\Trend Micro\HiJackThis\HiJackThis.exe
C:\Windows\system32\DllHost.exe

R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://www.google.it/
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 = http://go.microsoft.com/fwlink/?LinkId=54896
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = about:blank
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Local Page =
O2 - BHO: AcroIEHelperStub - {18DF081C-E8AD-4283-A596-FA578C2EBDC3} - C:\Program Files\Common Files\Adobe\Acrobat\ActiveX\AcroIEHelperShim.dll
O2 - BHO: Spybot-S&D IE Protection - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O2 - BHO: Search Helper - {6EBF7485-159F-4bff-A14F-B9E3AAC4465B} - C:\Program Files\Microsoft\Search Enhancement Pack\Search Helper\SearchHelper.dll
O2 - BHO: avast! WebRep - {8E5E2654-AD2D-48bf-AC2D-D17F00898D06} - C:\Program Files\AVAST Software\Avast\aswWebRepIE.dll
O2 - BHO: Java(tm) Plug-In 2 SSV Helper - {DBC80044-A445-435b-BC74-9C25C1C588A9} - C:\Program Files\Java\jre6\bin\jp2ssv.dll
O3 - Toolbar: avast! WebRep - {8E5E2654-AD2D-48bf-AC2D-D17F00898D06} - C:\Program Files\AVAST Software\Avast\aswWebRepIE.dll
O4 - HKLM\..\Run: [avast] "C:\Program Files\AVAST Software\Avast\avastUI.exe" /nogui
O8 - Extra context menu item: E&sporta in Microsoft Excel - res://C:\PROGRA~1\MICROS~2\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: Ricerche - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~2\OFFICE11\REFIEBAR.DLL
O9 - Extra button: (no name) - {DFB852A3-47F8-48C4-A200-58CAB36FD2A2} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O9 - Extra 'Tools' menuitem: Spybot - Search & Destroy Configuration - {DFB852A3-47F8-48C4-A200-58CAB36FD2A2} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O11 - Options group: [ACCELERATED_GRAPHICS] Accelerated graphics
O16 - DPF: {20A60F0D-9AFA-4515-A0FD-83BD84642501} (Checkers Class) - http://messenger.zone.msn.com/binary/msgrchkr.cab56986.cab
O16 - DPF: {5AE58FCF-6F6A-49B2-B064-02492C66E3F4} (MUCatalogWebControl Class) - http://catalog.update.microsoft.com/v7/site/ClientControl/en/x86/MuCatalogWebControl.cab?1277899387939
O16 - DPF: {5D6F45B3-9043-443D-A792-115447494D24} (UnoCtrl Class) - http://messenger.zone.msn.com/MessengerGamesContent/GameContent/it/uno1/GAME_UNO1.cab
O16 - DPF: {C3F79A2B-B9B4-4A66-B012-3EE46475B072} (MessengerStatsClient Class) - http://messenger.zone.msn.com/binary/MessengerStatsPAClient.cab56907.cab
O17 - HKLM\System\CCS\Services\Tcpip\..\{B602877E-3176-45D2-843A-097B281B52A4}: NameServer = 193.70.152.15,193.70.152.25
O17 - HKLM\System\CS1\Services\Tcpip\..\{B602877E-3176-45D2-843A-097B281B52A4}: NameServer = 193.70.152.15,193.70.152.25
O17 - HKLM\System\CS2\Services\Tcpip\..\{B602877E-3176-45D2-843A-097B281B52A4}: NameServer = 193.70.152.15,193.70.152.25
O23 - Service: avast! Antivirus - AVAST Software - C:\Program Files\AVAST Software\Avast\AvastSvc.exe
O23 - Service: FLEXnet Licensing Service - Acresso Software Inc. - C:\Program Files\Common Files\Macrovision Shared\FLEXnet Publisher\FNPLicensingService.exe
O23 - Service: Servizio Google Update (gupdate) (gupdate) - Google Inc. - C:\Program Files\Google\Update\GoogleUpdate.exe
O23 - Service: Servizio Google Update (gupdatem) (gupdatem) - Google Inc. - C:\Program Files\Google\Update\GoogleUpdate.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - C:\Program Files\Common Files\InstallShield\Driver\1050\Intel 32\IDriverT.exe
O23 - Service: MBAMService - Malwarebytes Corporation - C:\Program Files\Malwarebytes' Anti-Malware\mbamservice.exe
O23 - Service: NBService - Nero AG - C:\Program Files\Nero\Nero 7\Nero BackItUp\NBService.exe
O23 - Service: NLS Service (nlsX86cc) - Nalpeiron Ltd. - C:\Windows\system32\NLSSRV32.EXE
O23 - Service: SBSD Security Center Service (SBSDWSCService) - Safer Networking Ltd. - C:\Program Files\Spybot - Search & Destroy\SDWinSec.exe

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End of file - 4807 bytes

Grazie ancora davix, il computer va molto meglio, ho anche disattivato in strumenti-servizi i programmi che non erano utili all'avvio.