Problem with PHP, MySQL and Apache System

Hi all! I do not know, if this is the right forum, but I need help ..... We have a stable Website, that handeled several thousand visitors a day before xmas. We did some additional programming (mostly PHP) and are running into problems right now, that can be reproduced, but we do not know where they come from: Server-side: Linux, Apache, PHP, MySQL Client: Windows 2000, IE 5.5 Surfing the site is fast and traffic is very low today. After surfing around for some minutes and trying to open a new page i just get back a blank page, the browser tries to load the page but finally, a "site not found" appears. This happens with all pages ... When i Restat my browser after closing all windows, everything is fine. Does anybody have a clue, what could be wrong? My knowledge on PHP and MySQL is medium, on Apache it is almost zero... Any tips are appreciated! Thanks Christian