You can do 2 things

1st thing-Sometimes they block an ip which might be allocated you via DHCP by your ISP.

Reset your connection - you will get a new IP and the site will open.

2nd thing - is change your DNS server entry to 8.8.8.8

I face these problems often not with PTfiles(I am not a member) but other sites.

I resolve the issues following the above mentioned steps.

Let me know if it worked for you