If it's a work computer, your employer's IT department will have to deal
with it.

If it's a home computer, I would show it to a professional. If you're
feeling brave, try scanning your system with /several/ of the better
online scanners, such as:
Kaspersky Antivirus (http://www.kaspersky.com/virusscanner)
Panda ActiveScan (http://www.pandasoftware.com/activescan)

HijackThis is a program that searches your computer for signs of
infection. The program produces a detailed log that you can submit to
volunteer experts for analysis. (The Microsoft public newsgroups do
/not/ offer this service.) More information:
http://www.whatthetech.com/hijackthis_v2

---
Leonard Grey
Errare humanum est

If the machine doesn't belong to your co-worker, neither of you should
attempt to "fix" it.  Call your IT department.

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.
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.

On-line scanners are the most unsafe and next to useless. Because by the
time you've started your infected Windows and connected to the
Internet via this infected code base, and start to look for scanning sites
through infected DNS, you are almost certain to have the malware
perfectly positioned to overrule your attempts to clean it.
What happens if active malware is found? Don't expect that the on-line
scanner will do anything about it. Most of them are just just marketing
tools for selling you their products. Quite often, malware removal on the
NT based OS (Win 2K and XP) is far from easy. Sometimes a (good) resident
AV can deal with it in Safe Mode.

David's Multi-AV is *better and safer*, because you don't have to be
on-line to use it (it has no dependencies on using a web browser to perform
its function), and it can be used in Safe Mode.

Download David H. Lipman's MULTI_AV.EXE from the URL:
http://www.pctipp.ch/ds/28400/28470/Multi_AV.exe
http://www.pctipp.ch/downloads/dl/35905.asp
English:
http://www.raymond.cc/blog/archives/2008/01/09/scan-your-computer-with-multiple-
anti-virus-for-free/
When the menu is displayed hitting 'H' or 'h' will bring up a more
comprehensive PDF help file.
Additional Instructions:
http://pcdid.com/Multi_AV.htm

I have finally had time to search for "Multi AV Scanning Tool by David H.
Lipman"  but cannot find anything about the program other that "posts" that
people have made in the various message boards, etc.  Who is David H. Lipman?
Should I trust his program not to screw up the computer...?