The following command, which can be execute from xampp on a windows PC, will help you assertain if you communications with PayPal are getting blocked.

From PayPal

We have recently seen contacts from merchants whose host IPs got blocked by an ISP in-between PayPal and the host, effectively blocking them from reaching PayPal. we do not block these IPs ourselves, this is an issue outside the scope of our company.

You could execute ( or ask your network administrator to do so ) the following commands and send the results to your admin (or host) for further analysis, this will help them to find a definitive fix for this situation.

openssl s_client -connect www.paypal.com:443     (or the endpoint URL you use to connect to PayPal)

Links

• What are the IP addresses for Live PayPal servers? - The IPs used by our systems can be found here
• Going Live with Your Application - PayPal Developer - Also please have a look at this guide