It could be a corrupted Cache, a browser hijacker or one of those strange IE things that happen.
Download a free copy of Firefox browser at
http://www.mozilla.com/en-US/firefox/ Try getting to the sites that are causing you problems. If this works ok then the problem is in IE.
If there is a problem with IE then try this: clear your history, temporary files (these will take a while!) & cookies, restart the computer and retry.
If none of these work you may have more serious problems. Let me know how it goes.