One computer on my network can't access a website

I checked all of the usual: hosts file, firewall, AV, peerblock, etc. Nothing suspicious. Every computer on my network except this one can get to it just fine. I've tried different browsers and cURL, no luck anywhere. It always just times out. Any ideas? The strangest part is that its intermittent. I had no problems accessing it this morning or yesterday mornings but it dies halfway through the day.

Edit: I double checked, and its resolving to the right IP, and tracert gets it all the way there, but I get no response. Checked my router logs, and it sends the request just fine, but this particular PC gets no response at all whereas the others do. It's almost as if their server is ignoring my http requests but I'm not sure what's different about the requests sent from this PC. It can't be useragent...

Edit 2: Now it works fine..... I'm sure it'll cut out again

hmm maybe its network card is on its way out? you have already checked everything else i would have suggested. maybe try to uninstall its network card/reboot and re install clean drivers for it never know could be a driver conflict / corrupt drivers.