Use the IE 6 repair function in Add/Remove programs to see if this solves the problem, you can also download the Opera browser (More professional and secure then Firefox, although Firefox 2 is slowly starting to get there) and try that. (Malfunctioning Firewalls etc can also cause problems)
If the above fails, open up a DOS Box and then do a TRACERT to see what servers seem to cause the problem, if it stops at your modem, note down all the details you have set up in it, and then reset it to OOTB to see if this clears the problem, also make sure you have the latest Firmware for your modem, (Don’t forget that any electronic unit can become faulty) if it is an external server problem then notify your ISP.
Hope this helps

Bill