Sounds like you have a bad case of spyware (especially since your home page keeps changing).
I would recommend running an application called AdAware (Adaware home Page or Spybot search and Destroy (Spybot's Home page ). Make sure after you install these applications, to update to the most recent DAT files. Once installed, perform a check on the pc and see what it finds. I would run the application a few times to make sure everything gets cleaned. Once the pc is cleaned, then I would also recommend to run a virus scan. There's been a few nasty ones out on the internet recently.
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