I used to just go to the website I wanted to use, go to internet options, on general tab click use current, click apply and then Ok. It changes when I use the Home button but not when I first log onto the internet.
More aboutchange internet startup page windows
I haven't used IE in a long time. There may be a seperate setting for the start page. Check the options.
If not, you may have some malware on your system that is taking you to some product's or service's site.