I suspect you're seeing the effects of a hijackware infection
which either cannot be detected by your security apps or which has disabled
them completely.
Unexplained computer behavior may be caused by deceptive software
http://support.microsoft.com/kb/827315
Chances are you will need to seek expert assistance in
http://spywarehammer.com/simplemachi...php?board=10.0,
http://www.spywarewarrior.com/viewforum.php?f=5,
http://www.dslreports.com/forum/cleanup,
http://www.bluetack.co.uk/forums/index.php,
http://aumha.net/viewforum.php?f=30
MS PCSafety provides home users (only) with no-charge support in dealing
with malware infections such as viruses, spyware (including unwanted
software), and adware.
https://support.microsoft.com/oas/default.aspx?&prid=7552&st=1
If these procedures look too complex - and there is no shame in admitting
this isn't your cup of tea - take the machine to a local, reputable and
independent computer repair shop.