There are a lot of possible reasons a VPN won't work. You really need to see a log message that reports the connection problem to be able to fully diagnose the issue. Does your VPN client produce log files? If not can they be enabled? Can you ask your work IT dept to check logs at their end?
One possible reason for a previously working connection to fail is if your IP address has changed, and is now in a prohibited range (possible because it used to be registered overseas) - so has your IP address changed? If you look your IP address up on a whats my IP website does it report its location as being overseas?
