Hi
Is that Modem is a Router?
If you have the computers connected to one Switch in the same Vlan and each has an IP address in the same Subnet, so you should be able to connect to them without any problems.
If you have multiple PCs connected to one switch, but in different Vlans, you need a router to reach them, and that could be using the Inter-Vlan Routing feature on the 5300 Switch.
Good Luck !!!