WHat Is bLocking vistaprint.com? ?

like you guys I've seen more strange things that anyone could count and dealt with most of them. this one has me stumped badly :-o

vistaprint.com will not load on one machine on the net! it will load/go on every other device [2 ipads, multiple cellphones/wifi, two win7 machines, etc].
no malware. [she's clean]
no problems with any other website that we know of.
same identical problem with IE8 [this is winxp sp3] and/or 32bit Chrome.
changed settings, checked and rechecked java installation, setup, etc.
nothing helps. I simply get the error screen "cannot load".

searching around the web, lots of people have had the issue since three/four years back, but the answers are awful... several technet posts about it, and the answers are all terrible [like "are you sure you're running IExx?", or "reset to defaults"]

something is blocking that particular site. we have the same version of AVAST on all the win machines, howbeit two are running win7 64-bit; the machine in question as said is winxp sp3 32-bit.
same net firewall. Windows on firewall is also enabled which is probably not necessary but unlikely the cause [same with other windows sys's].

tried safe mode & networking: same results.


clues?