Seeing Laptop on Network Comes & Goes

Hi,

I have a desktop with Windows 7 and a laptop with Vista both with a wired connection to my router.

After working fine for years and transferring information back and forward, my laptop now disappears from the network from time to time. When this happens I cannot see my desktop from the laptop either. I could go back half an hour later and everything is back and I can see all network devices from both machines. Next time I look laptop is gone from desktop network and the laptop shows nothing other than itself.

This is very frustrating so can anyone advise what may be causing this please?

Axel