You could download and try using this browser (if you aren't already)
http://www.mozilla.com/en-US/firefox/
If you use Internet explorer, in the top bar, go to tools, then internet options, then privacy tab, then advanced. You may need to change the settings there for how cookies are allowed and handled (such as checking "allow session cookies"). You may need to experiment to see which settings fix your problem.
You may also find some thing to help you here http://www.google.com/cookies.html
Or download the latest version of Internet Explore here http://www.microsoft.com/windows/products/winfamily/ie/default.mspx