Intermitent login, internet,and E-mail

Having problems with intermitent logins, e-mail, internet access, and printing. Some users can log onto the network some cannot and it changes. The same goes for internet access, E-mail and printing. Starting to belive im losing some peice of hardware on the network possibly a hub, switch and/or router. Is there anyway to test to see which piece of hardware it is. Maybe a freeware or shareware program to map or test hardware connections? ANy help would be most appreaciated.