Hey donaldje and welcome to MyCE.
The official language in this forum is English and not many understand Dutch at all so you may wish to write your posts in English in the future. :flower:
I have not seen a program called HPS for file sharing, is it like FTP?
Anyway, all the PCs behind the router have an internal address 192.168.x.x, while the internet connection only has one IP, as you said 84.x.x.x. This is called Network Address Translation (NAT). So if you want the resources of one of the PCs to be accessible from the Internet under the 84.x.x.x address, you need to do port forwarding (see the manual of the Linksys router or www.portforward.com for help on how to do it). The port for FTP servers is 21.