A few points / Solutions. Firstly, You may be able to speify this site as safe somewhere in Avasts settings in which case Avast will the cease to block access. Secondly there may in fact be a virus on the site in which case you should dig a little deeper (google 'avast showing virus on www.xxxxx.com' - should give you some answers and solutions, xxx being the site name). There are other free anti-virus solutions - google 'free anti virus software for windows' then uninstall Avast and downlaod and install a different one. Personally stop using Windows, its really prone to viruses and VERY insecure. Try using LINUX instead - VERY secure, NO VIRUSES, MUCH faster, and best of all FREE. There are loads of different varieties of LINUX but a good one for people moving from windows is Linux MINT KDE. Its similiar to windows in look and feel. Here is a link
http://www.linuxmint.com/