It sounds like you have spyware and that your homepage has been hijacked.
Here are some free scans you try. I like ewido the best
Spybots search and Destroy http://www.download.com/3000-8022-10122137.html?tag=pao
adaware se> http://www.download.com/Ad-Aware-SE-Personal-Edition/3000-8022_4-10399602.html?tag=lst-0-1
http://www.webroot.com/land/freescan.php
a-squared Free> http://www.emsisoft.com/en/software/free/
http://housecall.antivirus.com/housecall/start_frame.asp
http://housecall65.trendmicro.com/
X -Cleaner Micro Edition scan http://www.spywareguide.com/onlinescan.php
http://www.kaspersky.com/virusscanner
http://www.windowsecurity.com/trojanscan/
http://www.bitdefender.com/scan8/ie.html
http://www.pandasoftware.com/products/activescan/com/activescan_principal.htm
http://www3.ca.com/securityadvisor/virusinfo/scan.aspx
http://www.javacoolsoftware.com/spywareblaster.html
Spywareguard too.
http://www.javacoolsoftware.com/spywareguard.html
http://www.ewido.net/en/onlinescan/
SystemDoctor is rogue registry cleaner. It is designed to "fix errors" that cause PC instability and lag. However, the developers of this program have a LONG history of un-ethical tactics to acquire their customers. They get their spyware installed on your pc. Then, once infected, you'll be plagued with irritating false 'Windows-Like' popups. Their irritating by design. They hope you'll be so frustrated, you're willing to shell out $50 to buy SystemDoctor to remove it.