Unable to connect to FTP sites even with Windows Firewall disabled

I am unable to connect to FTP sites to download drivers from companies like Dell and HP which share their drivers via FTP.

I can download the drivers by changing the link to HTTP but this is a workaround rather than the resolution I'm seeking.

I have opened port 21 on Windows Firewall and disabled Windows Firewall without any success. Other computers on the same network are able to access FTP so it isn't an issue with the company firewall (I'm the sys admin so I know for certain it isn't blocked).

However, I'm still not able to access these sites. It seems likely that something else is blocking port 21, but I'm not sure what.

Can anybody lend a hand?

Thanks in advance.