Not sure what you mean by that . When you do a ipconfig on the pc's are you saying the default gateways on the nics are missing or are you saying for some reason the network stops working . First place to start obviously before reloading the switches is to look at the logs and decipher if there is anything strange going on or happened about the time the pc's stopped working , really hard to say could be anything from an infected pc or flapping links causing spanning tree type problems . Check to see if the roots for all your vlans are where you think they should be . Are you getting a large amount of topology changes on the lan , if so what is causing it .