PC Could not get correct IP while Mac yes

Hi,

We run a small business and have 4 WIFI routers throughout the whole premise. 3 of the WIFI routers hardwire connect to a DLink WIFI router via LAN ports. Then the DLINK hardwire connects to a DSL WIFI modem. So the DLINK is giving out the IP addresses.

Somehow since a couple months ago, all PCs could not get a valid IP address while all Macs, iPhones and iPads most of the time do not have that problem. However sometimes we had to Renew DHCP Lease to be able to get into internet.

For PCs, we had done some google for solution such as ipconfig / release & ipconfig / renew but had no effect.

So we are not sure where the problem is. For the customers with PCs we had to put manual IPs into their laptops that we became tech supports, which add extra work to our business. And I am at a point almost giving up.

And could someone recommend a router that can handle 50 devices (laptops, tablets and smart phones) pretty fast and is reliable that it is easy to manage and with zero to little maintenance?

The DLink is kind of slow. So I am looking into a replacement.

Thank you for reading this and I would appreciate any input. : )