network fail problem

dear sir
(1)we are facing a network problem in which first network goes slow then disconnet computers and when we switched off & on the switch problem solved but not from particular switch. network established between two buildings and we have two servers one is pdc in bldg no 3 and another in bldg. 13. our pdc is in building no. 13 and bdc in 3. bdc is used as a mailserver and pdc as database. and all mails on bdc.if require any detail contact me on my mail-id.

(2)some time 2-3 system hangin outlook, mail not open. sysem not hang same day.i checked with ping network working fine if we run any activity in hdd then mail work properly
waiting for your response.
thanx
deepak jain