Judging from similar posts here in the past month or so, the behavior may be
due to a Vundo-ZLOB-SDBot infection, all of which is protected by a rootkit.
If so, I'd very much doubt the machine's clean yet.

Unexplained computer behavior may be caused by deceptive software
http://support.microsoft.com/kb/827315

Run a thorough check for hijackware, including posting your hijackthis log
to an appropriate forum.

Checking for/Help with Hijackware
http://aumha.org/a/parasite.htm
  http://aumha.org/a/quickfix.htm
  http://aumha.net/viewtopic.php?t=5878
http://wiki.castlecops.com/Malware_Removal_and_Prevention:_Introduction
http://mvps.org/winhelp2002/unwanted.htm
http://inetexplorer.mvps.org/data/prevention.htm
  http://inetexplorer.mvps.org/tshoot.html
http://www.mvps.org/sramesh2k/Malware_Defence.htm
http://defendingyourmachine2.blogspot.com/
http://www.elephantboycomputers.com/page2.html#Removing_Malware

When all else fails, HijackThis v2.0.2
(http://aumha.org/downloads/hijackthis.exe) is the preferred tool to use (in
conjuction with some other utilities).  HijackThis will NOT fix anything on
its own, but it will help you to both identify and remove any
hijackware/spyware with assistance from an expert.  **Post your log to
http://aumha.net/viewforum.php?f=30,
http://forums.spybot.info/forumdisplay.php?f=22,
http://castlecops.com/forum67.html, or other appropriate forums for review
by an expert in such matters, not here.**

If the 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 (i.e., not BigBoxStoreUSA) computer repair shop.

==========================================

Start a free Windows Update support incident request:
https://support.microsoft.com/oas/default.aspx?gprid=6527

Support for Windows Update:
http://support.microsoft.com/gp/wusupport

For home users, no-charge support is available by calling 1-866-PCSAFETY in
the United States and in Canada or by contacting your local Microsoft
subsidiary.  There is no-charge for support calls that are associated with
security updates.
--
~Robear Dyer (PA Bear)
MS MVP-IE, Mail, Security, Windows Desktop Experience - since 2002
AumHa VSOP & Admin http://aumha.net
DTS-L http://dts-l.net/