I'd be very suspicious of a hijacker/spyware type program that may be on
your machine. I don't like that idea that something may have changed the
settings and then locked you out of there.
First:
I suggest you download a little program called Hijackthis. Go to this page
http://tomcoyote.com/hjt/#Top for instructions on its use and to download.
This will scan your computer and generate a log of everything that is
running.
Next:
Set up an account at Spywareinfo
http://forums.spywareinfo.com/index.php?act=idx
and post your LOG there, not here. There are many experts on that forum and
someone will analyze it and
let you know if anything is amuck and what you can do to fix it.
You always want to keep your virus definitions up-to-date as well as use
tools like Spybot and Ad-Aware which also must be kept up-to-date every time
*before* you use them to scan your machine.
Spybot
http://www.safer-networking.org/en/index.html
Ad-Aware
http://www.lavasoftusa.com/software/adaware/
If you need a good FREE antivirus try AVG at
http://www.grisoft.com/
This may sound like a lot of work and it is. And there's still no
guarantees. But, you'll learn a whole lot in the process.