I want to stop a site from popping up when I turn my computer on?

Answer 1

Get a pop-up blocker if one doesn't come with your internet service provider. Also clean the spyware off your computer, Download.com has Spybot and Ad-Aware and they can do that.

Answer 2

It sounds like you have spyware
Follow this advice:

1. Do not download anti-spyware programs blindly, they might be spyware themselves. Check this list to no which programs to trust:
http://www.spywarewarrior.com/rogue_anti-spyware.htm

2. Download the following (if you don’t have them already) and then UPDATE them. Scan with all these programs and then trash what ever they find. (some scanning may take a while)

Windows Defender
http://www.download.com/Microsoft-Windows-Defender/3000-12771_4-10598014.html?tag=lst-0-1

Spybot
http://www.download.com/Spybot-Search-Destroy/3000-8022_4-10401314.html?tag=lst-0-1

Superantispyware
http://www.download.com/SUPERAntiSpyware-Free-Edition/3000-8022_4-10597413.html?tag=lst-0-1

Ad-Aware
http://www.download.com/Ad-Aware-SE-Personal-Edition/3000-8022_4-10399602.html?tag=lst-0-1

If you’re using Internet Explorer, stop using it and use Firefox, this will you help with future problems:
http://secunia.com/graph/?type=sol&period=all&prod=12366
(keep in mind that nothing can help you if you purposely/accidentally download spyware)

Firefox
http://www.mozilla.com/firefox/

3. Stay away from porn, gambling sites, myspace and other risky sites.
http://blog.washingtonpost.com/securityfix/2006/07/myspace_ad_served_adware_to_mo.html