Saturation of CPU resources in Win2K

I have problems with several computers using Win2K. The CPU resources consumption increase to 100% in the process Explorer.exe and this produces the machines run extremaly slow and freeze by moments. I have uninstalled several softwares, I have checked for viruses and there are not viruses, I have checked for adware and there is no adware. These machines are networked and use a DSL to a permanent Internet connection. Have some of you some answer tothis common problem in Win2K?