PC off network

Hello Gurus. Here’s the short version of my problem:

I’ve got a desktop and a laptop. Both connect to my wireless home network via a Linksys router. After initial set up 2 years ago, both connected to each other by the same network. All though slow, I was able to transfer data back and forth and my laptop was able to access both the ext. HD’s and the printer hardwired to my desktop. All as it should.

At some point many months ago, I lost access between laptop and desktop, and vice versa. Can’t recall when or why. Both still access the internet wirelessly.

Laptop is old and slow so I complied with my wife’s wishes and recently got her a Macbook. It too accesses the wireless network and functions on the ‘net without difficulty. I set it up for file sharing and it immediately saw and connected to the laptop, and vice versa. Still no desktop showing up on either of them.

Sharing is enabled on all drives of each unit. What is my next move? Any help would be extremely appreciated.