sounds like you have some spyware on your machine that
has hijacked your homepage. Go to www.lavasoft.com and
download the free version of "adaware". When it's
downloaded (do it to the desktop), double click the icon
to run the setup. Then double click the new icon that is
installed to run the program, check for updates, then
perform a smart system scan and get rid of anything it
finds. (it does keep a record of what has been
quarantined if you need to restore anything later)

Other programs that are available include "spybot"
and "hijackthis" - do a search on google if you need them

HTH