Macbook Air stalls/hangs up

I have a Macbook Air, less than a year old. It stalls or hangs up when I either refresh a webpage or click a link in an article to go to a new tab and display that site. The only thing that sometimes works is to restart the computer. I reinstalled the operating system and it worked great for 2 days. Now, it's all hung up again.. hours later it finally loads the page.

Any ideas?

Thanks

Bb