You have to check diagnose on presence any viruses -because scanning by using installed protected software is not credible -many viruses can hide before these program the better way use external tool - I recommend
Malwarebytes.org
if nothing wrong find follow to below steps:
Run cmd.exe with administrative previlliges and type
sfc /scannow
when it will done create report
Run cmd.exe with administrative previlliges and type
findstr /c:"[SR]" %windir%\logs\cbs\cbs.log >%userprofile%\Desktop\sfcdetails.txt
on your desktop appear file
sfcdetails.txt
next run CheckSur
http://support.microsoft.com/kb/947821
even if this tool won't resolve problem automatically it create logs:
C:\Windows\Logs\CBS\CheckSUR.log
System also create logs -there is log
C:\Windows\WindowsUpdate.log but this log is mostly too big
So download FireGenUL
Altair Technologies Ltd.
place this file in
C:\Windows\System32 and restart computer
next run cmd.exe and type
firegenul
and then will create short *.htm report from WindowsUpdate.log placed in C:\Users\<your account> -report name
FireGenUlReport.htm
All tree files:FiregenUlReport.htm,sfcdetails.txt and CheckSUR.log pack them and attache to post -if they will are to big to attache upload them on
Speedy Share - upload your files here