Download Malwarebytes' Anti-Malware, which is free from http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html, and install it.
Run a quick scan, and remove any infections.
Hopefully, you then shouldn't have an issue.
Don't bother installing Ad-Aware or Spybot unless it doesn't resolve the issue. Malwarebytes is much faster, and detects much more than both of the other ones put together!