Winxp Pro computers disappear from Network Places

I have a network of five computers, all windows xp pro, no servers or domains, and all in same workgroup. Static IP (manually configured, not DHCP). When I restart my pc I can see all of them in Network Places, then after about 20 minutes, 3 of them (including mine) disappear. I can ping them, and still access mapped drives but can not see them in network places. I have checked ipconfig, ran cdiag, and browstat. XP firewall is disabled, I have KIS 7.0 and tried with and without it disabled with same results. The network has run fine for about 2 years, then about 2 weeks ago the PC’s start disappearing.

If you need more info let me know. Thanks in advance for any help.