Sounds like a Virus or Spyware.
You can try this online site, it's a good starting point for cleaning and speeding up your system, Windows Live Online Scan (free):
http://onecare.live.com/site/en-us/default.htm
I highly recomend you have at least one of each of these types of software installed on everyone's computer:
Anti-spyware program
Pop-up blocker
Anti-virus program
Firewall
ANTI-SPYWARE PROGRAMS:
It's important to note that the spyware programs jostle around a LOT as to who is the "best" one... no single one program gets everything out there, so I think it's best to have at least 2 or 3 spyware programs running on your machine. I really like Microsoft's spyware program since it is the only one which
(without paying for a professional version) will keep itself updated automatically and can be set-up to run automatically. Also, if you find spyware on your computer using one of the programs run that program again since spyware can often hide other spyware from showing up.
Microsoft Windows Defender:
If your running XP, 2000, or Vista (not ME, 98 or NT) this is a great program.
http://www.microsoft.com/athome/security/spyware/software/default.mspx
Ad-Aware:
This program is one of the best ones out there. It's free for home use however you have to tell it to update regularly or is isn't useful. If you want to purchase a copy it can keep itself updated. Since I suggest running spyware removal program at least once a week:
http://www.download.com/Ad-Aware-SE-Personal-Edition/3000-8022_4-10045910.html?tag=txt
Spybot Search and Destroy:
This was the best for a long time, however they haven't been ranking as well recently. It is still Free and well worth downloading for the immunization option which will keep some spyware from ever getting on your system in the
first place. The advanced features are *great* for advanced users, but not easy for everyone to understand.
http://www.download.com/Spybot-Search-Destroy/3000-8022_4-10122137.html?tag=txt
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POP-UP BLOCKER:
Yahoo! toolbar:
If you don't like pop-ups, this is a nice toolbar which also has some nice features. Note: if you are getting a LOT of pop-ups you may have a spyware program which is actually what is bringing them up, so I'd suggest running the anti-spyware tools again.
http://www.download.com/Yahoo-Toolbar-with-Anti-Spy/3000-2379_4-10310983.html
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ANTI-VIRUS PROGRAMS:
AVG anti-virus free edition:
This program is nice as a free anti-virus (I'd suggest buying an anti-virus program if you don't have one, but if you know someone who won't/can't at least have them use this program). It works well and has been getting good reviews, however doesn't compare to a paid one in many ways, harder to use interface, not always updated as quickly, etc..... If you want a second anti-virus program this is good for that though:
http://www.download.com/AVG-Anti-Virus-Free-Edition/3000-2239-10342876.html
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FIREWALL:
ZoneAlarm:
Best free firewall out there. (Note: Vista and XP hava a firewall built in that you can turn on so you may already have a decent EASY TO USE firewall ). I think ZoneAlarm is better than many you can pay for. The only issue is the initial set-up since it's not super user friendly. I would suggest the professional paid for version for a novice (or ask a computer geek to help you initially set it up). Otherwise I find it best to install the software and go through each of the programs you have the use the internet (Internet explorer, outlook, instant message programs, etc....) and click allow (CLICK ALWAYS USE THIS OPTION CHECKBOX THEN ALLOW so you aren't asked all the time for those programs) for all of those. Then go through each of the programs you use that need updates from the internet regularly (Anti-virus, anti-spyware, etc) and tell each of them to update now so you can allow (CLICK ALWAYS USE THIS OPTION CHECKBOX THEN ALLOW so you aren't asked all the time for those programs) those programs as well. After you get through those programs you shouldn't get too many more requests. After this initial set-up it's easier to use. If you get a pop-up that asks if you want to allow it to access the internet (when you first open the program, if it asks later deny it first or click for more information) and it is a program that may need internet access it's usually safe to click allow, otherwise click deny and see if a program you are using stops working (if everything seems to be working then it's fine to always deny that program if you see it ask again a few more times). If your
program stops working, close it down and open it again and you should be asked if you want to allow it, at this point allow always.
http://www.download.com/ZoneAlarm/3000-10435_4-10388719.html?tag=lst-0-1
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If it's not a virus, this site may help you optimize your computer better, PC Pitstop (free):
http://www.pcpitstop.com/
You can also considering adding more RAM as it can speed up your computer overall. Also, sometimes bad hardware or software can cause your system to act funny as well.