Putting today's machines into closed spaces accelerates not only the fans but the aging process to help spur more PC sales. Your choice here.
I own a Dell "tower" model computer for a few years now and have always had it under my desk but out in the open office air. I recently purchase a large L shaped office desk with a cabinet for the computer and a power management console. I noticed that when the computer is running in the cabinet (which has a few 3" diameter holes in the back in side, the fans in the computer go into high speed mode. When opening the compartment I can feel a significant amount of heat. It defeats the purpose of having this setup if the computer is going to burn up unless I leave the compartment door open. Is it okay to let the fans run on high and leave the cabinet closed?