If you're using Internet Explorer, and are experiencing a slowdown in addition to your wierd popups where there shouldnt be, you might have a 'browser hijacker' that can be removed with a program called cwshredder from Trend Micro. www.trendmicro.com/cwshredder/ I want to note that the last time I brushed up against a browser hijacker, it blocked access to removal tools. So you might need to get the utility through a different computer.
Then, try using a Mozilla browser (the latest browser is called "Thunderbird"):
http://www.mozilla.org - less vulnerable. Well, it's not vulnerable at all to browser hijackers, to my knowledge. Which is a big reason to use it as your default browser. But Mozilla browsers are groovy anyway. Here's why they make for a better web surfing experience:
Bookmarks are saved in a regular html file instead of the less-portable shortcut format IE uses. The print preview funciton is very nice. It lets you resize your print so it fits on a page! You can have several web pages open in one browser window via "tabs", which de-clutters your taskbar. Mozilla also allows you more control over javascript functions - for example, my browser ignores commands that turn off the right-click button on my mouse. Try that in IE! I can also successfully save pages in Mozilla that fail to save in IE.
Finally, Mozilla is open-source software. Its products are a continuation of the Netscape browser, after Netscape was bought by AOL.